A dead treasurer. £86 missing. A receipt for somebody else's letter. Wrackmouth, a fishing town on the north-east coast of England, December 1958. On the first morning of the month, the treasurer of the chapel Christmas Club is found at low tide below the Quay Steps. £86 is missing from the club box, and the town has already decided she took it. 1,200 registered letters. 24 days. 1 killer. In her bag is a receipt for somebody else's registered letter, soaked purple in the harbour. Post office clerk Nellie Tamsley has copied every registered letter the office took in during 1,200 lines. One of them is the letter on that receipt. How it works Read one day. 24 dated chapters, 1 to 24 December, each with its own notebook page and an upside-down hint. No doors to one chapter a night.Strike the November Book. Each chapter ends with one thing the receipt has given up. Cross out every letter it rules out, and check your count against the Checkpoints.Name the killer on Christmas Eve. Three letters are left. Their senders each say one thing. Exactly one of them is false, and the November Book shows which two are true.Inside A 24-chapter mystery, set in 1958 and checked against the Post Office of the registration fees, Christmas Day post, copying-ink pencilsThe November 1,200 registered letters to check against the cluesCheckpoints for every day, a hint for every day, and full answersFour Christmas logic grids from the post-office queue, as a bonusExactly one solution, checked a second time from the printed pages. Every one of the 24 readings is needed.No app, no website, no download. A pencil is all you need. From the author of Signed at the Gate. You don't need to have read it first.