Cassie Lenue is an orphan who doesn't know who her parents are. She grew into a con artist and according to Sherlock Holmes, one of the best liars he's ever met.
|Watson and Holmes meet Cassie while investigating a case of a girl, Mina Davenport, who returned to her family after being kidnapped for over ten years. Sherlock deduces that Cassie has been posing as Mina. Cassie meets them in private and tells them that Mina was killed by her parents and that she will help them prove it as long as they don't reveal her secret as it will allow her to access Mina's $5M trust fund. Holmes tricks her into planting a bomb in the Davenport's home which allows the police access to DNA and they find the blood of a missing FBI agent in a car. All are incredulous that the DNA test shows Cassie is related to the Davenports but Holmes is able to deduce that Cassie found the real Mina and took her hair just before Cassie was "found." Cassie is arrested and while in a holding cell, she confidently tells Holmes that she believes she will be able to lie her way out of the situation in court. ("Miss Taken")|
|Holmes and Watson are surprised to find Cassie waiting for them on the steps of The Brownstone. Inside, Cassie asks a skeptical Holmes and Watson to find the murderer of Heather Foley, a foster mother, who was shot outside a kid's clothing store. Cassie claims Heather was her foster mother in an unofficial capacity. Holmes believes Cassie is lying but she still convinces them to look into Heather's case. Having asked for Bell's help, at the precinct, Bell tells Watson that Heather was shot with a 9mm pistol and he's reached out to detectives in NJ who were assigned the case. In exchange for looking into the case, Holmes tells Cassie she'll stay at the Brownstone, be under constant surveillance and gives her a phone which can only be used to call Holmes or Watson. He still believes she has an ulterior motive and says he'll find out what it is.
|Cassie and Holmes visit Heather's husband, Judd, who treats Cassie as an old friend even though they'd met only a week before. Cassie explains that Judd wasn't married to Heather when Cassie knew her. Judd reveals that weeks before Heather was murdered, she often left the house at night after receiving phone calls which Heather said was for her job. She worked for a baby formula service which Holmes remarks doesn't explain why she left at night. Judd believes she was having an affair but looking at Heather's computer, Holmes finds an email to a Meredith Sagehorn, Heather's buyer, in which Heather questions whether a formula seller was a thief. Outside Judd's, Holmes explains to Cassie that the formula seller was likely an undercover officer. They're met by Detective Owen Calabrissi and Detective Farrad who explain they are assigned to Heather's case, that the service Heather was working for dealt in stolen formula, that she was their informant and was killed when discovered.
|While at NJ State Police HQ, Holmes tells Cassie that he was able to gather all the information she used on Heather's background from online sources. Accusing her of running a con, Cassie says that Holmes doesn't understand her childhood isolation, that connecting with Heather was important to her and guesses that he had plenty of social interaction growing up. Watson thinks Holmes has a soft spot for Cassie. Holmes admits that Cassie has a unique talent which he'd like to see used for good. Looking for Cassie's true intention at the halfway house she stays at, Holmes discovers that all of her web searches involve unsolved murders.
|While watching a suspect being questioned at the precinct, Cassie is able to confirm the suspect is telling the truth. Holmes shows Watson the unsolved murders Cassie was researching. He believes the reason Cassie reached out to them is that she's searching for direction in life. In the kitchen, Holmes confronts Cassie why she came to him and Watson. She lies that she researched Holmes' family in order to steal from him. Knowing better, Holmes says she's lonely and looking to make a connection with him. Saying he's right, Cassie asks for his advice on what she should do with her life. Holmes offers to help figure it out with her.|
|After reviewing security footage at the HQ of Leehoven's, a retail chain with over 400 stores in NJ, Holmes tells Cassie that he believes someone killed Heather in order to stall the investigation into a formula mafia until after the senate vote on dropping formula from a NJ state program for low income parents. Discovering the owner of Lehoven's, Mack Lehoven, has the most to lose from the state dropping formula from the program, at night, Cassie breaks into Mack's home and after accusing him of arranging Heather's murder, she asks for $2M in exchange for her silence. Cassie sneaks back into the Brownstone to find Holmes waiting in her room. Learning from Everyone of her break-in, Holmes accuses her of betraying him and blackmailing Mack.
|Explaining that she set up a meeting for the $2M in order to draw out Heather's killer, she asks if Holmes would like to see who arrives. At the precinct, Detective Calabrissi is taken into custody while Watson explains to Bell and Gregson that he was Mack's fixer and provided details on the formula investigation to Mack. Given Cassie's role in solving the case, all three wonder about her future. At Cassie's halfway house, Holmes brings Cassie a form which she thinks is to find out who her parents are. Expressing no interest in learning about them, Holmes corrects her and says the form is an application to change her name, so that she can be defined by her future and not her past. Cassie asks if he'll help her think of some names. ("Miss Understood")
- "Lenue" stands for "LNU", a court acronym for "last name unknown."
- "The best liars often make the best lie detectors."
- ―Holmes to Cassie, "Miss Understood".
- "She possesses a singular intellect. It would be a shame to see it go to waste."
- ―Holmes, "Miss Understood".
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