|"Step Nine": After capturing an assassin of three U.S. Attorneys, a call on Holmes' phone results in him asking Watson to accompany him to London to help Gareth Lestrade, his old colleague. As they are packing, Holmes tells Watson his history with Lestrade. He calls him utterly adequate as a detective, but as credit for successes went to Lestrade, he began to crave the glory. At Scotland Yard, they are greeted by DCI Hopkins, Lestrade's superior. Describing the Mary Pendry case, in which Lestrade refused to let go of his suspicions and due to his extreme actions was suspended, Hopkins wants Holmes to find Lestrade. A cab delivers Holmes and Watson to 221B Baker St., Holmes's former residence in London. To his horror, he finds it has been totally remodelled and discovers that his brother Mycroft is living there. Sherlock finds Lestrade in a pub by tracking down various stashes of money that Lestrade knew about. Feeling guilty that he is responsible for Lestrade's addiction to fame, Sherlock agrees to look into the Pendry case. Sherlock finds that Mary's husband Lawrence did kill her using a plastic gun and is able to find evidence when Lawrence kills his handyman with the same weapon. Sherlock tells Lestrade that in order to break his addiction to fame, he is not to take credit for the arrest and if he does, Sherlock will discredit his involvement. The next morning, Sherlock and Watson see Lestrade on TV claiming the credit for Pendry's arrest. Mycroft texts Sherlock to meet him at a storage centre. He confesses that he didn't give away Sherlock's possessions but stored them at the centre. He says he learned from Watson that he must have Sherlock's attention when telling him something important and then blows up Sherlock's possessions using books on bomb building that were Sherlock's. Mycroft says he forgives Sherlock for everything and that things are different between them now.
"Solve for X": Watson visits the grave of Gerald Castoro, the man she accidentally killed during an operation. His son Joey Castoro arrives and presses her to have coffee with him. At a diner, Joey congratulates Joan on being a detective and she learns that he's dropped out of university, despite his father wanting him to become an engineer. Watson asks Holmes for an advance of $5000 to help Joey. He asks if she'd invest in a bar he's bought and applies some guilt tactics on Watson. She asks how much he needs. After mathematician Felix Soto is found murdered, Harlan Emple explains to Holmes and Watson that Soto was trying to solve P vs. NP. He indicates that another P vs NP expert, Tanya Barrett, may know who Soto's partner is. Questioning Barrett, Holmes finds the partner is Cyril Nauer who is found dead by Detective Bell. At the Morgue, Holmes recounts that Nauer was killed an hour after Soto and, by the same killer. Barrett becomes a suspect but when questioned, provides an alibi which is confirmed by time-stamped video. Confronting Barrett in her classroom, Holmes shows that she killed Soto and Nauer as they were close to solving P vs NP and she'd altered the security footage digital time stamp. Watson meets with Joey, and says she'll help him but will only pay for his education. Joey tries to guilt her into using the money for his bar but she remains firm.
"We Are Everyone": At The Brownstone, Holmes and Watson meet a new client, Mr. Mueller. Mueller says he represents a group of citizens concerned about Ezra Kleinfelter's safety, given that he has more secret documents he could leak. Mueller would like them to find and deliver Kleinfelter to him, so he can be taken to a friendly embassy. Holmes agrees to take the case and Mueller leaves. Having pick-pocketed a security guard's phone, who is connected to Ezra, Holmes discovers that he is a member of a cyber-activist collective "Everyone" and finds a message board, "Jamaica Quay." After Holmes wakes Watson, he reports that while debating on the board, he's deduced that a woman, Vanessa Hiskie, is hiding Kleinfelter. Watson picks the lock at Hiskie's apartment and they find her inside, dead. Having traced the security guard's phone to the Brownstone, Everyone subjects Holmes and Watson to a "life ruin". After discovering Ezra is leaving for Venezuela on a billionaire's jet, he arrested by Bell and Captain Gregson but is set free after threatening to reveal the identities of several deep cover federal agents. As Kleinfelter turns to board the plane, Watson grabs his wrist and warns him they will prove he killed Vanessa Hiskie. Watching the jet take-off, Watson produces Kleinfelter's wrist watch which she lifted from him. Impressed, Holmes asks Gregson to see if the DNA on the watch matches that found under Hiskie's fingernails. After Kleinfelter's arrest, Watson sits in bed with her laptop and begins writing "The Casebook of Sherlock Holmes."
"Poison Pen": Holmes and Watson are called to the home of Titus Delancey, CEO of a large financial firm, who was found dead in a bondage suit, by Mistress Felicia. Holmes discovers Titus was poisoned by nitroglycerin. Later, Holmes and Watson meet Titus' wife Peri and their nanny, Anne Barker. Holmes takes Watson outside and says that he knows her. She was the prime suspect in the poisoning death of her father, but was acquitted and her name was Abigail Spencer. In "the box" at the 11th Precinct, Gregson questions Anne who admits she was Abigail Spencer. She has no alibi but denies killing Titus. She changed her name and appearance to escape the media attention from her father's death, is angry that it will happen again and asks how they discovered her identity. Holmes says it was from her voice. Anne is released and Holmes believes that she is being framed. Watson deduces that Holmes didn't recognize Anne from her voice, but from a tattoo on her wrist. Impressed, Holmes relates that the poisoning of Anne's father catalyzed his interest in detective work. Holmes was able to deduce that she did kill her father, an abusive man, but only after the trial was over and she was acquitted. Despite this, he still believes that the framer must have discovered her past. Holmes visits Anne and reveals he is Sean Holmes. Beseiged by the media and fired as a nanny, she's still grateful to have Holmes to talk to. Bell and Watson find a tablet containing a video of Titus and Anne arguing.
"Ancient History": At a flea market, Watson and her friend Jennifer are shopping. Watson mentions that Holmes is bored, having no cases for weeks, and should introduce them one day. Hesitantly, Jennifer mentions she'd like to find a man she had a one-night stand with, Tony. Watson tells Holmes about Jennifer's request which he sees as demeaning. Pointing out that they are not busy, Holmes decides to find a case and takes Watson to the Morgue. Introducing her to Dr. Eugene Hawes, Holmes and Hawes play chess. Winning the game, Hawes gives Holmes access to the morgue's corpses. Hours later, Holmes comes upon the man who died in the motorcycle crash, Leo Banin. Holmes deduces that before Leo died, he killed someone. Watson visits the bar Jennifer met Tony at and discovers she met him on day of the Brazilian Parade. Holmes finds Watson about to watch a news tape showing the Brazilian Parade day at the bar. Unable to dissuade her, he admits that he is Tony. Shocked, she follows him to the kitchen where he explains that when she first started as his sober companion, he would follow her when she left for errands. Hoping to learn more about her, he saw her with Jennifer and passed himself off as Tony. He claims Jennifer seduced him and that once he found Watson's intentions as his sober companion were honorable, he stopped surveilling her. Later, Watson meets Jennifer to let her know that Tony was Holmes but she already knows. Holmes explained everything to her and so impressed, she slept with him again. However, Jennifer is totally over Holmes. At the Brownstone as Holmes practices with Bob, Watson unsuccessfully tries to scare Holmes that he's impregnated Jennifer.
"An Unnatural Arrangement": In the holding cells at the 11th Precinct, Holmes has Watson deduce what caused the prisoners to be jailed by examining them. After Captain Gregson's wife Cheryl is threatened during a home invasion, Holmes and Watson discover the attacker entered the wrong house. This leads them to pursue various members of a US military detail who were guarding an archaeological dig in Afghanistan led by Beth Roney. Roney stole various artifacts and with her ex-husband Cameron's help, tried to sell them. Holmes and Watson provide evidence her ex was behind the Gregson's home invasion and several others in which Cameron killed members of the military detail. Holmes gives Watson a box with files on cases he hasn't been able to solve.
"The Marchioness": Mycroft asks for help with an acquaintance of his and Sherlock's. At Diogenes, Sherlock is not happy to see the acquaintance and introduces Watson to Nigella Mason, Mycroft's former fiancée. Mason explains that after Mycroft, she married a Marquess. Not fulfilling his conjugal duties, she had an affair with Dalton, who was the stable master. The affair caused her divorce but she retained her title and a champion race horse, Silver Blaze. Dalton was killed by an intruder at the stables who intended to kill the horse and she'd like them to find Dalton's killer. Deducing that Mycroft and Watson slept together when they were in London, Sherlock is protective of Watson. Sherlock captures Dalton's killer, an assassin nicknamed "El Mecánico" and finds that Nigella's troubles were her own doing after she fraudulently passed off another horse as Silver Blaze for studding a drug king's mare.
"Blood Is Thicker": Sherlock and Watson solve a case involving the murder of tech billionaire Ian Gale and his estranged daughter Haley Taylor. Both were killed by Ian's doctor wife, Natalie, for his estate. Mycroft unsuccessfully tries to lure Sherlock to return to live in London after Sherlock discusses the possibility with Watson.
"On the Line": Holmes and Watson thwart serial killer Lucas Bundsch and frees several women being held captive while dealing with a disgruntled detective, Gerry Coventry. Holmes punches Bundsch and breaks his finger. Holmes discusses Watson's rebuking of his lack of politeness with others. Although he understands the social benefits, he indicates he is not a nice man, never will be and that being acerbic helps his work. Watson points out that he is often nice to her and that he has changed since they first met, but Holmes demands that she accept that there will always be fallout from his behaviour.
"Tremors": Holmes and Watson are subjected to an administrative hearing pertaining to a case in which Detective Bell is shot. Prosecutor Cassandra Walker accuses them of breaking the law in the course of investigations. As they recount the events in solving the murder of Silas Cole, Holmes' arrogance brings retribution from a suspect, James Dylan. As Dylan tries to shoot Holmes, Bell intervenes and is hit. Bell is partly responsible for the decision to allow Holmes and Watson to continue to work with the NYPD.
"Internal Audit": While investigating the murder of a corrupt hedge fund manager, Gerald Hauser, Watson re-meets Chloe Butler, who she was a sober companion to. Watson resists revealing Butler's past addiction, even though it would help the Hauser investigation. Holmes and Watson prove that Hauser was killed by Jacob Weiss, a charity CEO. Weiss and Hauser were partners in the scam but when Hauser's pyramid scheme was discovered, he told Weiss that he'd revealed the embezzlement.
"The Diabolical Kind": When a seven-year-old girl named Kayden Fuller is kidnapped and her father shot, Holmes and Watson hear the ransom demand. Holmes quickly recognizes the voice as that of the man who previously pretended to be Moriarty, who Moriarty herself described as one of her subordinates. Assuming Moriarty gave the order for the kidnapping, Holmes and Watson visit her at a prison black site. She's made a large painting of Watson's face in perfect detail. Moriarty denies being involved in the kidnapping, but offers to give information in exchange for prison favors. Holmes refuses, but shortly afterwards discovers she has been recruited as a consulting agent by her FBI handler, Ramses Mattoo, who bring her to work with the NYPD. Moriarty provides information on the kidnappers and is accompanied to the kidnapping scene by Watson. Moriarty admits she finds Watson more intelligent and interesting than at first, and that part of the reason that she and Holmes write to one another is because they are the only ones who can understand and relate to the other. When the kidnappers ambush and kill two policemen, Holmes believes Moriarty is somehow responsible. Devon Gaspar, one of the kidnappers and a former Moriarty lieutenant calls and puts a frightened Kayden on the phone. Watson notices that Moriarty is angry when listening to the call. Moriarty is returned to her prison cell. Holmes discovers code in the sketches Moriarty made of the kidnappers but is surprised to find that Moriarty isn't behind the kidnapping she's a victim as Kayden is her daughter. Moriarty escapes her prison using glass shards of her paint jars to neutralize her stun bracelets (cutting her wrists badly) and strangles Mattoo unconscious. She tracks Gasper and the kidnappers down in an old building she owns and kills them all. She calls the police and demands that Holmes be the only one sent into for her. She tells Holmes that Kayden has been re-situated and she placed her for adoption knowing that knowledge of Kayden's existence would make her vulnerable. Moriarty believes she will soon be free and thanks Holmes for his letters. She begins to pass out from blood loss so Holmes carries her outside for treatment where Watson believes she will recover.
"All in the Family": After Bell departs the 11th for Demographics, Holmes and Watson deal with a number of incompetent detectives, including Detective Nash. At a recycling plant, Bell finds a headless, handless body in a green barrel and calls for Gregson. Bell is icy towards Holmes so Watson excuses themselves. Holmes notes the barrel's original color was blue and from a scar on the man's leg, Watson knows who the man is. In Gregson's office, he's identified as former mobster Bobby Pardillo. At Demographics, Holmes offers his and Watson's services to Commissioner Frank Da Silva. Seeing Holmes, Bell is irked to learn Holmes will be working there when Holmes knows Bell doesn't want to see him. Holmes belittles Bell's new role as an analyst and leaves. At the home of a suspect, Dante Scalice, Holmes and Watson witness him die when his car explodes. Finding printouts at Scalice's which show Bobby's movements, Holmes recognizes them as from the NSA. Holmes and Watson confront Dean McNally who denies being part of the NSA. Later in private, McNally indicates to Holmes that Da Silva asked for the printouts. Finding evidence that Da Silva is corrupt and worked for the mafia, Holmes and Watson have a difficult time convincing Bell. After Bell finds further evidence that Da Silva is dirty, Bell and Holmes set a trap in which Da Silva is caught planning to murder a mob boss. Bell returns to the Major Cases unit and makes up with Holmes.
"Dead Clade Walking": At The Brownstone, Holmes is surprised to find a guest in the library, Gay. Watson explains that while examining Holmes' box of unsolved cases, she found the murder of Doug Newberg, in which a picture of his backyard had an unusual rock. Without permission, Watson and Gay enter Newberg's backyard and find the rock still there. Gay says the rock is from the dinosaur era and likely contains an archaeological specimen. Holmes meets Watson at the Morgue where a technician performs a CT scan on the rock. A complete skeleton of a small dinosaur is discovered inside it. At the Triboro Museum of Natural History, they meet with Dr. Jerome Thomas by a Dimetrodon skeleton which he indicates is the only complete one in the world. After the fossil is stolen from the precinct, Holmes meets with C. who informs him that a man known only as the "Magpie" buys rare, expensive items and that if Holmes posts such as item on a website, the Magpie will reach out to him. On the way to the "Magpie's" home, Holmes tells Watson that Randy isn't answering his phone. Finding the door open, they enter and discover a dead man and the nanotyrannus rock smashed on the floor. At the Brownstone, Holmes wakes Watson and believes he's found the motive for smashing the fossil, a theory called "Dead Clade Walking" (DCW). At the museum, Holmes and Watson confront Dr. Jerome Thomas and accuse him of destroying the fossil and committing the murders as the fossil's existence would discredit Thomas. He's served a warrant for his DNA to match that on a murder weapon.
"Corpse de Ballet": At the scene of a bisected ballerina, Nell Solange, Gregson leads Holmes and Watson through the crime scene and reports that the killer took the hard drive containing the security videos. A box cutter belonging to ballerina Iris Lanzer is the murder weapon. Questioning Lanzer, Holmes is uncharacteristically polite and deferential and, he offers explanations for many of his colleagues questions. Watson gets a call from a shelter she volunteers at that one of their clients is off his meds and had a run-in with the police. At the hospital, two officers explain their altercation with Morris Gilroy who is restrained in a bed. Gilroy yells that a sergeant named "Freebo" was taken. Watson calms him and promises to find Freebo. Watson identifies "Freebo" as former Army Sergeant Zeke Frebeaux and Bell agrees to distribute his picture to NYPD cars. Watson talks to Rachel Brown, who says she's Zeke's sister, at her house. Saying that Zeke has PTSD from service in Afghanistan and drug problems, she brought him home to care for him, but he wouldn't stay. She doesn't know where he is but as Watson indicates that she'll keep looking him, Brown expresses her gratitude. Gilroy is back on his meds, at a shelter and as Watson gathers clothing to bring there, Holmes asks why she's going to so much effort to help him. Watson reveals that her genetic father is schizophrenic and homeless. She volunteers at shelters hoping to see him. At the shelter, Gilroy tells Watson that he saw a white man rough Zeke up and take him away in a van. Watson indicates she hasn't found Zeke and his sister hasn't seen him. She looks through Zeke's bag and finds a pack of cigarettes which she noticed at Rachel Brown's. Looking at a family photo, Gilroy points to Zeke's sister who isn't Rachel Brown. At Rachel Brown's, Watson arrives with police and asks for Zeke. Rachel and her husband Cliff lie that Zeke isn't there. With a warrant, they enter and find a padlocked door. Zeke and two other men are found chained in the room. The Browns were collecting their veteran and disability checks.
"The One Percent Solution": "The One Percent Solution": At The Brownstone, Watson arrives and finds Holmes has broken up a cock fighting ring. He's feeding two roosters, Romulus and Remus and intends to experiment if they can be trained to stop fighting. Gregson calls them to the scene of the explosion which killed several people from the Dept. of Labor (DoL) and a bank whose CEO is Richard Balsille. Gregson informs them that Balsille has a "security czar" they'll have to work with which, to Holmes' revulsion, turns out to be Gareth Lestrade. Holmes discovers Lestrade is arranging sexual partners for his employer, CEO Richard Balsille, and catches the bomber, MoL staffer Michelle Forrester. Fired from his job, Lestrade asks if he can stay at the Brownstone while Holmes' experiment with the roosters is a success.
"Ears to You": His confidence shattered, Lestrade is mugged and has difficulty picking a new job, despite several offers. Encouraged by Watson to solve the case of his mugging, Watson and Holmes deal with a case involving Gordon Cushing, whose wife Sarah disappeared years before. Receiving a package containing Sarah's ears, a ransom demand goes wrong and Holmes and Watson are baffled to find Sarah alive, with her ears intact. They discover her new husband, a plastic surgeon, grew ears on her back which were removed and used in the ransom demand. After finding his mugger, Lestrade believes that Holmes doctored the case to boost his confidence and seeing through Holmes' "ruse" has done the trick and he's accepted one of his job offers. He threatens to stay unless Holmes admits to the charade. Holmes shakes his hand, congratulates Lestrade and heads to the kitchen. Confused, Watson follows and asks Holmes why he didn't let her in on his plan. Holmes honestly says he's never heard of the mugger nor seen the mugging file but wanted Lestrade to move on.
"The Hound of the Cancer Cells": After Barry Granger is murdered at a laboratory, the head of the lab, Hank Prince, shows Holmes and Watson what Granger was working on, a device called "The Hound" that could detect lung cancer from breath. Without Granger and combined with an anonymous tipster who refuted the device's test results, Prince is ruined. Later, they show Prince who was behind the fake allegation and that Granger's work has been cleared. Believing that he and Granger may be the victims of corporate sabotage, Prince provides them with a list of rivals to "The Hound." Prince's wife, who he was divorcing, is then found dead. They discover that Prince discredited the Hound and killed Granger, which would temporarily lower his company's value, so that his wife wouldn't receive as much in the settlement. Once Holmes and Watson cleared the allegation against "The Hound", Prince killed his wife so she wouldn't share in its value. After much reflection, Holmes meets Bell at a party celebrating Bell's return to active duty.
"The Many Mouths of Aaron Colville": Watson learns of a "vampire killer" who bites his victims from Detective Loughlin and remembers from her time as a surgeon, Aaron Colville, a serial killer who also bit. After taking a plea deal, Colville died in 2005 during a surgery Watson was a part of. She visits Dr. Jonathan Fleming, who refuses to tell her what Colville whispered to him before he died. With the help of Everyone, Holmes gets dental records and match them to vampire killer's bite. They find that Colville's teeth were the model for dentures issued at Newgate prison. After finding a good suspect, prison dental assistant Stan Kovic, he's cleared of the murders. Watson confronts Fleming again who admits that Colville whispered that he'd killed two women. Watson tells Holmes about Fleming's confession which leads him to believe the killer knew about the dentures and wanted to cast doubt Aaron was the killer. Holmes and Watson discover Aaron's mother Ruth is the killer and find a copy of Aaron's dentures at her house.
"No Lack of Void": Watson heads to the 11th Precinct where she's asked by Captain Gregson to look at a prisoner, Apollo Mercer, who has collapsed in a holding cell. She discovers Mercer has died from anthrax poisoning. Holmes reviews videos and tells Watson that Alistair died the week before of a heart attack. Gregson asks Watson and Bell to visit Eugene MacIntosh, brother of a suspect, Bart. Eugene indicates where Bart may be which Watson relates to Holmes. After seeing a case loaded into the truck, he breaks in and discovers the case is filled with jars of white powder. Two men surprise him and in the struggle, he subdues them, but they are all covered with the powder. Later at a hospital, Watson meets Holmes who is miffed he's being tested as the powder was baby powder. Watson is angry Holmes took such a big risk when a police team was minutes away from the truck. The next morning, Watson confronts Holmes that he lied to her about Alistair who died of a heroin overdose. After an outburst from Holmes, she presses why he lied. Initially, Holmes says it was to protect Alistair's privacy but he eventually admits that Alistair helped him when he was high, something most recovering addicts wouldn't do. After Bart kills his brother Eugene, seemingly in self-defense while claiming he was poisoning his cows with anthrax, Watson and Bell discover Bart poisoned his cows for an insurance payout while trying to pin the poisoning on Eugene.
"The Man With the Twisted Lip": Mycroft returns to NYC and asks Watson out to eat at Diogenes while Sherlock and Watson search for a missing woman, Paige Dahl. At Diogenes, Mycroft proposes dating Watson and while she's interested, she's worried it would makes things with Sherlock difficult. At a park, Watson finds Paige dead in the woods while Sherlock finds a dead man, Zach Piller, against a rock. Sherlock is puzzled by shotgun blasts on the rocks around Piller and, the appearance of a mosquito, though it's winter. At Piller's former workplace, Sherlock and Watson find Piller worked for a company that makes drones. At Diogenes, Sherlock tries to stop Mycroft from dating Watson and takes a picture of a man he noticed there before. As Sherlock shows her the photo of the man, de Soto, who is a lieutenant in a French crime organization, Le Milieu, Watson expresses her anger at him interfering in her relationship with Mycroft. Believing that Mycroft is involved with Le Milieu, Sherlock then bolts out of his chair, grabs a glass and captures something on a table. Hearing clinking, he explains to Watson that he's captured a tiny surveillance drone. He now knows why there was a strange shotgun pattern around Piller's body, he and Paige were killed by drones. At Diogenes, Watson expresses her interest in dating Mycroft but indicates that she'll have to move out of the Brownstone first. She also sees a man, Marchef, who was sitting at the same table when she met Mycroft earlier and she takes his picture. At the precinct, she now agrees that Le Milieu is using Diogenes as a base and shows Sherlock her picture of Marchef who is linked to a massacre. Watson break into the office of an executive of the company Piller worked for while Sherlock meets the executive. They are able to prove that the executive ordered Piller to carry out a drone strike in Afghanistan which killed CIA operatives, then covered it up and had Piller killed. Watson heads to Diogenes where she's kidnapped by Marchef.
"Paint It Black": Marchef informs Watson that Mycroft will be helping them or she will die. Watson hears screaming and discovers from Marchef that his cousin, Jem, has been shot. Since Marchef won't take him to the hospital, she offers her help. Having operated on Jem, Marchef warns Watson that if Mycroft fails, he'll still have to kill her. Watson tries to care for Jem who has gone into shock. Marchef tells her that it was Mycroft's idea to use Diogenes as Le Milieu's base. Having done everything she can for Jem, Watson tells Marchef he needs a hospital or he will die. To Watson's shock, Marchef shoots Jem in the head. His phone rings with news that Mycroft has succeeded and she'll be exchanged for the list. The exchange location is under an overpass where Mycroft alone meets de Soto, Marchef and a number of Le Milieu men. After providing the list and Yoder, de Soto orders Marchef to kill Mycroft and Watson and drives away. Unable to persuade Marchef to spare them, Mycroft is granted last words with Watson. He says "paint it black" and shots ring out killing Marchef and his men. Several black SUVs race onto the scene and British black ops soldiers secure the location. Mycroft tells Watson he has much to explain to her.
"Art in the Blood": At the Brownstone, finding guards and Watson being attended to by a doctor, a furious Sherlock turns on Mycroft and believes Mycroft is being arrested by British Intelligence only to be told that he works for them. Meeting Mycroft's handler Tim Sherrington, he debriefs Sherlock on the rescue of Mycroft and Watson from Le Milieu and that they needn't be worried about repercussions. To Mycroft's surprise, Sherrington asks Sherlock to work on a case of an ex-MI6 analyst, Arthur West, who has been murdered. Over Mycroft's objections, Sherlock agrees to look into West. Returning to the Brownstone, Sherlock discovers that Watson wants to work so he fills her in on West's case. At the Morgue, they discover that Arthur's arms are missing. Arthur's wife, Marion, eventually reveals she tattooed numbers on Arthur's arms in infrared ink and gives them a picture of the tattoos, which are all numbers. She doesn't know what the numbers mean and that Arthur was convinced there is a mole in MI6. He did say the mole was selling secrets to a bookstore owner, Julian Afkhami. Sherlock deduces that the data represents dates and times, but to what, he doesn't know. Watson tells Sherlock that she's moving out of the Brownstone which he thinks is a knee-jerk reaction to her kidnapping. Explaining that she's planned it for a while and that she needs a life outside of detective work, he's stunned into silence and then leaves. Watson goes to Mycroft's apartment and asks him to explain about a man named Sudomo Han. After Mycroft left MI6, Han employed Sherlock, at the height of drug use, as a courier of trade secrets. However, Sherlock didn't know he was aiding Han in financing a terrorist plot. The plot was thwarted but after Sherlock's involvement was discovered, MI6 pressured Mycroft into returning to work in exchange for Sherlock not going to jail. Sherlock knew nothing of this and realizing how much Mycroft sacrificed for Sherlock, Watson kisses him. In bed at Mycroft's, Watson tells him that she's moving out of the Brownstone and that Sherlock didn't take the news well. Sherlock calls Sherrington and says he knows who the mole is. Breaking into Mycroft's, Sherlock catches them in bed and tells Mycroft that he's being framed for murder and treason.
"The Grand Experiment": At a safe house, Sherlock believes a mole in MI6 is framing Mycroft. He's told MI6 what he knows but also said that Mycroft is the mole. He hopes this will gain MI6's confidence and while pretending to work with them to find Mycroft, that he'll find the real mole. Sherlock meets MI6 Deputy Chief, Sir James Walter and Mycroft's handler, Tim Sherrington, but is unsuccessful in gaining access to their files. He lies that he'll let them know when he finds Mycroft. Sherlock and Watson break into Julian Afkhami's store and Sherlock finds a scrambler that Afkhami could use for certain calls. Arthur West wouldn't have understood the calls but Sherlock believes he would know the date, time and location of them. At the safe house, Sherlock examines the info West had tattooed on his arms. Although burner phones would have been used by Afkhami's contact, the code of the cell tower used would be part of the metadata of the call. Sherlock realizes this is what West tattooed on his arms. As he reads the locations and dates, Mycroft confirms that he was at locations. Watson deduces that Sherrington was also there and that he is the mole. Sherlock finds that the dates correspond to events that benefited Iran and that Sherrington provided secret information to make the events occur. While Sherlock is called to the precinct, Sherrington visits Watson at the Brownstone and threatens her. However, she's prepared for this and has various members of Everyone witness Sherrington's threatens via monitors in the the media room. At the safe house, Sherlock wakes Mycroft to tell him about Watson's encounter with Sherrington and, that he knows why he re-joined MI6. He's confused why Mycroft would make such a sacrifice when he owed Sherlock nothing but Mycroft simply states they are brothers. Sherlock vows to fix the Sherrington situation. After Sherlock and Watson find evidence that Afkhami killed a man who was having an affair with his wife, Gregson tells Sherlock that Afkhami gave Sherrington up. Sherrington turns up dead and Gregson tells Bell to put out a Finest Message for Mycroft. At the Brownstone, Sherlock and Watson confront Mycroft who says he didn't murder Sherrington. He contacted NSA Agent McNally who he traded MI6 secrets for the NSA arranging for Sherrington's murder. Sherlock deduces that the NSA has faked Mycroft's death which he confirms. Mycroft will have to disappear which he tries to apologize to Watson for. She leaves, frustrated and upset. Sherlock indicates that they were working on a solution for him that would take hard work which isn't Mycroft's way. Mycroft interrupts Sherlock's chastisement by hugging him, proclaiming his love, and then leaves. Eavesdropping outside Watson's bedroom, Sherlock hears her making an appointment to view an apartment. Distressed, he retrieves a hidden stash of heroin. He then visits Sir Walter and agrees to work for MI6.