When fellow passengers on a ship bound for London start to disappear, Miss Withers must rely on a mischievous cat to help solve the mystery. Schoolteacher and occasional sleuth Hildegarde Withers has not had good luck with vacations. On her last trip, she found herself enmeshed in the investigation of a dead man on a small plane. Now, on a three-day steamer voyage to London, she's about to encounter death again.   A gruesome joke leads to a young woman going missing from the ship's aft rail. Is she somewhere onboard, or has she fallen into the sea? In either case, turning about will do nothing for her, so the ship steams on. Soon the passengers descend into a nightmare, as body after body appears. Putting an end to the chaos falls to Miss Withers, who must depend on the testimony of a particularly mischievous silver Persian cat. The teacher and the feline will make it to London safe and sound--so long as their curiosity doesn't get the best of them.   The Puzzle of the Silver Persian is part of the Hildegarde Withers Mysteries series, which also includes The Penguin Pool Murder and Murder on the Blackboard.