Related Clues:

• German cipher machine used in the Second World War
• Mystery in game, possibly, e.g. man I exchanged
• Ciphering system cracked by Alan Turing
• Hard-to-crack puzzle
• Puzzle's unusual meaning when noun's omitted
• Force in Maine novel provides a type of mystery
• Perplexing puzzle
• You!
• Real puzzle
• Puzzle-solving in game
• Mysterious sort
• Mystery when head of gold found in a hole pulled up
• Puzzle in mag cracked after second of sessions
• Hemingway ignores why this is hard to fathom
• Inscrutable puzzle