A young woman is found murdered in her apartment with a strange symbol painted on her mirror. Meanwhile, Castle and Beckett are lured along with others into a trap where they must solve mysterious puzzles to escape.
- Angsty Surviving Twin: Brandon's scheme was triggered by the suicide of his twin sister Fay.
- Driven to Suicide: The trauma resulting from her parents' experiments led Fay to recently take her own life, which triggered her twin brother Brandon to set up his own experiments with test subjects of his own.
- Freudian Excuse: Brandon's parents subjected him and his twin sister Fay to a series of psychological experiments when young, traumatizing them and leading Fay to take her own life. Brandon, who had previously failed to get help from the authorities, then set up his own experiments so that others would feel the same pain as him.
- Revenge by Proxy: Some of the kidnap victims were chosen just based on their occupational association with those who wronged Brandon.
- Patricia worked for the education department, which Brandon felt had failed him and his sister.
- When a young Brandon reported his parents to the police, officers from the 12th Precinct responded, talked to his parents, and then left, and Brandon was subject to more isolation as a result. Castle points out the absurdity of kidnapping Beckett for this, given that she was only a child when that happened.
- Sadistic Choice: The escape door has three levers, forcing each couple to choose who goes free and who gets left behind. When both Castle and Beckett choose to stay behind and expose Brandon as the mastermind, he pulls out a shotgun and forces them to choose who dies. Castle chooses to Take a Third Option and whacks Brandon with one of the levers that he quietly loosened.
- Schmuck Bait:
- All of the male subjects were lured with the promise of an inheritance or in Castle's case, an opportunity to work with Stephen King.
- In Beckett's room, the cigarettes Meadow was about to smoke were filled with peanuts, which she was allergic to.
- The revolvers in each room had their barrels plugged so that it would backfire on anyone who pulled the trigger, as Simon unfortunately found out.
- She Knows Too Much: An unusual example. Emma was murdered because Brandon felt that exposing his parents' experiments on TV didn't go far enough and the story would just end up getting ignored, unlike his planned story of murder-suicide.
- Spotting the Thread: When Brandon asks how Castle and Beckett figured out he was behind the mind games, Castle noted that he didn't even flinch when Simon pulled the trigger, and they both saw how eager he was to trigger the final door trap.
- Villainous Incest: Implied. Brandon regarded his twin sister as his soulmate, and after she died he wanted to make other couples feel that pain as well.
- Wounded Gazelle Gambit: As part of gaining the male subjects' trust, Brandon deliberately triggered his own anaphylactic allergy so that they would work to save him.
