He has armies on his payroll. He has mercenaries on speed dial. There are countries that you learned the name of as a child, that no longer exist because of him!
— Sherlock about Morland
At the scene of a diner robbery and shooting, Detective Bell reports that there was one survivor, Jordan Lee, but Watson shows interest in shooting victim Emil Kurtz and asks Bell to find out what order the victims were shot in. Outside the diner, Sherlock demands to know why Watson is interested in Kurtz and has been secretive lately. She confesses that she's been meeting Kurtz, who worked for Morland, was a mole in his organization and she believes that he was the target of the shooting. At The Brownstone, Sherlock is angry with Watson for becoming involved in his father's world, having warned her many times how dangerous he is. She explains that she trusts Sherlock completely, except for matters involving Morland, and that one of them needed to find out what he was up to since the man who attempted to kill him, Ruslan Krasnov, was broken out of jail. Sherlock indicates he'll mention their suspicions that Morland arranged for Kurtz's murder to Captain Gregson.
This is the scene of an assassination.
At Morland's office, Sherlock delivers the news of Kurtz's murder to Morland in order to ascertain if he was responsible. Asking for all materials Kurtz was working on, Morland refuses and Sherlock ominously says he'll find out who is behind the shooting. Bell and Watson question the shooting survivor, Jordan Lee, who gives them a partial description of the shooter. As Watson looks at the medical file of Jordan's sister, Angela, who died of anaphylaxis shortly after the shooting, Jordan says Angela was allergic to mountain lions. Sherlock makes Gregson aware of their suspicions concerning Morland and even though Gregson feels that Sherlock shouldn't be involved in the case, he allows him to work on it and says he'll trust that Sherlock will act lawfully. Watson meets Sherlock at Kurtz's condo where Sherlock has found numerous listening devices. Believing the shooter was a taxidermist, Bell calls that they've found a suspect.
Are you familiar with the term umwelt?
In "the box" at the 11th Precinct, Arthur Tetch confesses to killing Kurtz after being shown overwhelming evidence against him by Bell and Gregson. Fully cooperating in exchange for a deal, he says that a Mr. King visited his taxidermy shop and offered him money for the hit. He'd leave instructions where the target would be and arrange for them to be there. He mentions that King hired him to kill Patricia Naylor before he killed Kurtz. Meeting ADA Eric Madison, he tells Gregson, Sherlock and Watson that Naylor worked as a psychiatrist for the DA's office and would evaluate competency of defendants to stand trial. He's never heard of Morland so while Watson looks over Naylor's cases, Bell and Sherlock plan to visit her office. Gregson pulls Sherlock aside and after commenting on the odd fashion that Tetch was recruited, he tells Sherlock that he's going to meet Morland to size him up.
I'll tell you about the guy.
At his office, Morland denies knowing Tetch nor Naylor and tells Gregson that despite Sherlock's suspicions, he wasn't behind the murders. Gregson warns Morland that if anything happens to Sherlock or Watson, he'll exact punishment beyond the law. Reviewing Naylor's files at her office, Bell and Sherlock find no suspects. Speaking to Naylor's research assistant, Dr. Warren, she mentions that they were given a research grant and she's there to help Naylor's replacement with the transition. At the Brownstone, Sherlock shows Watson that Naylor and Warren had created a survey, the Depravity and Atrocity Numeration Test or DANTE, that measures responses to revolting questions. Intending it to be applied to heinous crimes, they hoped to create standardized sentencing guidelines. Sherlock believes that someone who took the survey objected to its intentions and killed Naylor.
Are you asking me questions as if I were a suspect?
Morland arrives and provides everything Kurtz was working on. Admitting he had discovered Kurtz was a mole and was feeding him misinformation to determine who he was working for, he knows they think he's behind the murders. Showing them encrypted emails Kurtz used with his employer, including one telling him to go to the diner, Watson recognizes the email address from her earlier investigation into Kurtz. If verified, Sherlock realizes this will vindicate Morland. Later at Morland's office, Sherlock informs him that Everyone has verified the email address but couldn't find who is behind it. Days previously, Morland startled Watson at the Brownstone and he explains that he was looking for an antique ring he'd stored there which Sherlock denies having seen. Morland shows Sherlock a file on a Colombian oil deal he lost which caused him to suspect there was a mole in his organization.
You threatened to expose him?
Morland blackmailed the CEO of the company who won the deal to reveal who gave him the information, but the CEO insisted it was received anonymously and he resigned in response to the blackmail threat. Knowing the CEO would have given up Kurtz if he'd know he was the mole, Morland proposes they work together to discover Kurtz's employer. Having gone through Tetch's computer, Bell tells Watson they discovered that he took the DANTE survey, even though he claimed to not have known Naylor before being hired to kill her. Confronted in prison, Tetch tells Bell, Sherlock and Watson that he took many surveys for fun and didn't know Naylor was involved in DANTE. Later at the Brownstone, Watson finds Sherlock taking the DANTE survey. (♫ Vicki Sue Robinson - Turn the Beat Around ♫)
Why are you listening to disco?
Explaining that after looking into Morland's files on the oil deal, he discovered that a bomb scare resulted in the value of Colombian oil stocks increasing. Sherlock's found that the perpetrator of the bomb scare also took the DANTE survey and he believes that it's being used to find people who lack empathy and are willing to commit violent crimes. Later, Watson tells Sherlock that Bell and a police team are executing a search of Naylor's research lab. Having retrieved the ring his father was looking for from a hiding place, he tells Watson that it was his mother's, May. Morland was looking for it to use as a bribe to discover Kurtz's employer and Sherlock has no intention of giving it to him. He also tells Watson that Morland showed him that May was a drug addict and it has him pondering how much biology is a factor in his own addiction.
Struck me as odd that he ever held onto it.
Dr. Warren is called to the precinct where she's shown that police have discovered that she has been isolating psychopathic responses to the survey, and then sharing the IP addresses of those respondents. Her bank records confirm she received six payments and she emailed her benefactor that Naylor was becoming suspicious of her just before Naylor was murdered. Warren breaks down and confesses, indicating she was approached by a man with CIA credentials who told her she'd be helping to recruit people for special missions. Eventually, when she realized the people were connected to murders, she was too scared to stop supplying the information. Asked if the man called himself Mr. King, she says he identified himself as Agent Babbage. Sherlock abruptly leaves and as Watson follows him, he pulls her into an empty room. Recognizing the names were math chairs at Cambridge, he's seen these types of pseudonyms used before, by Moriarty.