Martinnote Ennis is taken to the hospital under guard where he is to donate a kidney to his gravely ill sister. They sedate him, take off the cuffs, and prepare to perform the surgery when he suddenly opens his eyes, and kills everyone in the room (doctors, nurses and security) before escaping. Sherlock is taken to the scene and deduces that Ennis had pulled out the IV, and used a meditation technique to lower his heart rate. He also notes a word written in blood on the wall and recognizes it as a star. At the station he puts the constellation over a map of Manhattan to predict when Ennis will strike next, but then dismisses that as a red herring.
He then goes to tell his new theory to Gregson. Ennis intends to lay low, alter his appearance, and go back to killing. Sherlock discovers that he will be working with FBI profiler Kathryn Drummond, a former colleague whose profile led to Ennis' arrest. Since Drummond presented a similar theory, Gregson believes them. Unfortunately, this couldn't be further from the truth. Ennis approaches a woman in convenience store who fits his victim profile, only to kill the other two occupants, and have the woman take a picture of him next to a newspaper that shows he does not look any different. Kathryn Drummond claims that he did this for money, but Sherlock tells her that he is mocking her.
Tropes:
- Alone with the Psycho: Holmes goes out of his way to be alone with Ennis, to test Drummond's theory about him, hoping that she would be wrong about them both.
- Chekhov's Gun: Holmes gives Watson a brief rundown of the continuity errors in the porno her sub-letter made. Watson later uses one of those errors to prove that her landlord was in on it.
- Even Evil Has Loved Ones: Ennis breaks loose to wreak havoc and get revenge against The Profiler, Kathryn Drummond, because her book destroyed his family. She falsely alleged (and bribed an old neighbor to claim) that Ennis was sexually abused by his father, who later hanged himself. His mother died shortly after. His sister helps him break out of jail by deliberately inducing kidney disease. Holmes does speculate that Martin manipulated his sister to help him with this plan, but Ennis nevertheless takes time during his rampage to call Kathryn and tell her that his parents were good people who had nothing to do with what he has become.
- Nice Job Breaking It, Hero: Invoked regarding how Drummond's false profile is the reason for Ennis's latest killing spree. While Holmes concedes to Drummond's observation that Ennis didn't need a reason to kill, he nevertheless affirms that Ennis didn't have this reason until Drummond provoked him.
- Noodle Incident: After some amateur porn actors used Joan's spatula in their production, Sherlock gives her a new one and a toothbrush to replace her old one. Joan notes she didn't see them touch this in the final film. Sherlock notes they didn't. He is quiet on the rest.
- The Profiler: Kathryn Drummond is one and a former partner (in more ways than one) of Holmes. It's also something of a Discussed Trope, as the episode analyzes whether a profiler can be a legitimate detective or if they're just "snake oil science". It ends on a ambiguous note about their effectiveness.
- Relative Ridicule: There's a disturbance at Patricia's home, which Sherlock and Joan investigate. It turns out that her neighbors threw rocks through her windows when news coverage of her brother's recent escape and rampage helped them make the connection between the siblings.
- Roaring Rampage of Revenge: Ennis' motivation is that he wants revenge on FBI profiler Kathryn Drummond because she falsely accused Ennis' father of sexually abusing him, which led to the death of both Ennis' parents. His sister is in on it too.
- Serial Killer: Ennis who had killed blonde women by skinning them. He then breaks out of the hospital when donating a kidney and shoots up a convenience store, deliberately sparing a woman that fits his typical victim profile.
- Siblings in Crime: Patricia Ennis was in on her brother Martin's plan to get back at Kathryn Drummond. She poisoned her liver so Martin could escape when donating his, and then tried to kill Drummond with a pair of scissors.
- Skewed Priorities: Joan finds out that her sub letter directed a porno in her apartment while she was away. Sherlock watches it and is appalled... by the continuity errors.Sherlock: If I were you, I wouldn't be upset that a dirty film was produced in your home. I would be upset that it was produced so poorly.
- Sophisticated as Hell: Sherlock is definitely this. See "The Deductionist", where he describes serial killers as "onanists" (which is a really roundabout way to say jerkoffs or wankers), and in "Déjà Vu All Over Again" when he tells Watson that "opinions are like ani" (plural of anus, or asshole).
- Take That!: Sherlock reveals that he loathes behavioral profilers. While she was right to a certain degree, her insistence that Ennis was abused as a child drove his father to suicide.
- Theory Tunnelvision: Drummond admits later on that she automatically profiled Ennis as a victim of childhood sexual abuse because she'd profiled many past serial killers and found similar patterns in their childhoods. Rather than admit that she was wrong about Ennis after his capture, she goes so far as to pay a childhood neighbour to provide false testimony.
- Working with the Ex: Sherlock has to work with his ex-lover FBI profiler Katherine Drummond when an escaped serial killer is on the loose. He isn't happy at all with this arrangement, though.
