- Alice Allusion: A subtle one: In the human chess game at the beginning of the episode, Number Six is the white queen's pawn—the same position as Alice in Through the Looking-Glass.
- Armor-Piercing Question: Six's methodology for finding out who is a guard and who is a prisoner.
- Brainwashed and Crazy: The Queen of Hearts is convinced she's in love with Six in order to make her a better spy.
- Hoist by His Own Petard: Six actually screws himself in this episode as his entire strategy is based around most people not being as unbreakable as himself. So the fact he is unbreakable means his collaborators decide he's one of the guards.
- Wham Episode: According to Patrick McGoohan, the third in correct chronological order of the seven episodes that "really count".
Recap / The Prisoner E 9 Checkmate
Number Six has a brainwave about how to discover which of his fellow Villagers are prisoners, and uses it to form an escape committee.