Cain’s Jawbone, one of the more demanding puzzles of the 20th century, was recently solved for the third time. Devised by the inventor of the cryptic crossword, Edward Powys Mathers (aka Torquemada), it was first published in 1934. Perhaps inevitably, it has taken another crossword buff to crack it in 2020: John Finnemore sets puzzles for the Times under the moniker Emu (when he isn’t appearing in his own Radio 4 comedy series). Cain’s Jawbone isn’t a crossword, however, even if it has some of the same cryptic, sideways logic. It’s a whodunnit mystery novel with a structural twist, in that its 100 pages appear out of sequence, making the plot unintelligible and obscuring the identities of the murderers and their victims. The task is to find the correct page order, working out in the process who dun what to whom.