Cain's Jawbone is a murder mystery puzzle written by Edward Powys Mathers under the pseudonym "Torquemada". The puzzle was first published in 1934 as part of The Torquemada Puzzle Book. Crowdfunding publisher Unbound published a new stand-alone edition of the puzzle in 2019 in collaboration with the charity The Laurence Sterne Trust. Both editions, when published, were accompanied by a competition which offered a cash prize to the first reader to solve the puzzle. Cain's Jawbone has been described as "one of the hardest and most beguiling word puzzles ever published."