Samantha Wabash is standing on a bridge on a stormy night, trembling in fear. She pulls a gun and a dumbbell out of a bag, shoots herself, and the gun is dragged under the water by the dumbbell. Sherlock and Watson arrive at the scene. While Gregson believes it was murder, Sherlock notes scratches on the otherwise brand new railing. He notes the awkward angle the victim was shot at, and concludes she used a weight to drag down the gun.
At the precinct, a suspect named Lucas Bundsch is being interrogated. Bundsch was believed to be guilty of the murder of Samantha's sister Allie. Bundsch is subjected to questions with a polygraph and passes them. Then a policeman comes in and tells them that they found a weighted gun in the river, confirming Sherlock's theory. Before Bundsch leaves, Sherlock asks him about Allie Wabash, then shakes his hand. Sherlock becomes worried about Bundsch, and thinks that he killed Allie Wabash and possibly other women. He points out that he noticed the way Bundsch was biting his tongue to establish a baseline and used deodorant to remove sweat from his palms. He talks to Gerry Coventry, the detective who investigated Allie Wabash's death. Coventry still believes that Bundsch was innocent.
Back at the brownstone, Lucas Bundsch shows up at the door. Sherlock politely greets him, but secretly grabs a knife just in case. Bundsch still maintains his innocence, reminding them that Allie Wabash made a call after Samantha saw him carrying a fridge that she thought had her inside. After he leaves, Sherlock and Watson find footage of Allie Wabash making the call. Sure enough, she is alone. Watson notices that Allie has a limp, and suggests a broken ankle but Sherlock thinks something is in her boot. When they read the notes that a private detective took, they notice two things he found in his trash: a putty substance that resembles plastic explosive and a broken alarm clock.
They find another victim of Bunsch's, a girl named Bonnie Tilden, through a memorial site. They call her mother Cynthia, and she tells them to meet her at a gas station. When they arrive no one shows. They receive a call from Bunsch taunting them, and assume the worst. They call the local police and quickly head to her house. When they arrive, Cynthia is surprised the police showed up. According to her, she never had a daughter. They realize that Bundsch tricked them with a false persona.
Sherlock goes to Bunsch's studio and furiously accuses him.
Tropes:
- After Action Patch Up: Joan takes a look at Sherlock's broken finger after he punches Bundsch.
- Alone with the Psycho: Holmes confronting Bundsch in his recording studio.
- Framing the Guilty Party: Samantha Wabash fakes her own murder to frame her sister's killer. Later, Sherlock considers planting evidence, but has a "Eureka!" Moment that leads to an arrest before going through with it.
- Jerk with a Heart of Jerk:
- Detective Gerry Coventry resents Holmes' Brutal Honesty when they're publicly arguing about Lucas Bundsch's guilt (although Holmes was right to criticize him)—so much so that he gives Holmes and Watson's address to Bundsch, who promptly tries to intimidate them. (Hey, Bundsch was exonerated—even though Holmes and Watson think he's a Serial Killer—so no harm done, right?) Later, Gregson finds Coventry Drowning His Sorrows and gives him a What the Hell, Hero? speech.
- Holmes has a speech, describing himself as one.
- Lie Detector: Bundsch passed a polygraph when accused of killing Samantha's sister and asks to take another one to prove he didn't kill her. When Holmes watches the test he realises Bundsch is using several techniques to trick the machine such as biting his tongue on control questions and coating his fingers with deodorant. Gregson does point out that polygraphs aren't admissible in court specifically because their results are so unreliable.
- My Death Is Just the Beginning: The episode starts with Samantha Wabash faking her own murder in an attempt to frame her sister's killer.
- My God, What Have I Done?: Sherlock proves that Samantha Wabash made her suicide look like a murder to frame Lucas Bundsch, whom she believed killed her sister. Eventually, Sherlock realizes that Bundsch is a Serial Killer who has claimed many victims, including Wabash's sister. Fortunately, once again Holmes and Watson prove their case.
- Mythology Gag: Samantha's method of suicide being staged to look like a murder, on a bridge, with a weighted gun is taken directly from "The Problem of Thor Bridge".
- Nice Job Breaking It, Hero: Samantha Wabash kills herself to frame Lucas Bundsch, whom she believes killed her sister. Sherlock proves that it was indeed a suicide, but during the polygraph test realizes that Samantha was right in suspecting Lucas of killing her sister. He spends the rest of the episode trying to finish Samantha's work.
- Serial Killer: Lucas Bundsch kidnaps women, keeps them in a secret compartment where he abuses and kills them, and then leaves there bodies cut up. Despite being referred to as a serial killer through out the episode, the end actually reveals that he technically does not meet the criteria, as one of his three prior victims was discovered alive after being kept in a cramped room and tortured for years before being rescued at the end of the episode.
- Starts with a Suicide: The episode opens with Samantha Wabash shooting herself.
- Thanatos Gambit: Samantha's plan to frame Bundsch for killing her to get the police to investigate him. Sherlock almost disrupts the plan but once he works out what Samantha was trying to do he dedicates himself to bringing Bundsch to justice.
- What the Hell, Hero?:
- Watson and Gregson frequently talk to Sherlock about his bad behavior and his ego.
- Gregson to Coventry in regards to giving Bundsch Sherlock and Joan's address.
- Worthy Opponent: Lucas Bundsch, the serial killer. He manages to fool Holmes and Watson on several occasions and is so disgusting and dangerous that Holmes loses his control when confronting him.
