Drury Lane's Last Case (Drury Lane, #4)

A heavily disguised, anonymous man hires (now) private investigator Inspector Thumm to hold a sealed envelope him indefinitely; stating it holds "a clue to a secret" on which he is working. The man will phone Thumm monthly to let him know he is OK, and if he fails to phone on schedule, Thumm is to open the envelope in the presence of Drury Lane.

Meanwhile, a mystery is developing at New York's small Brittanic Museum. A bus tour of 17 Indiana schoolteachers, driven by George Fisher, had toured the museum. It is discovered two men had stowed away on the bus, and later a museum display case is found smashed. At the same time, museum guard Donoghue has disappeared.

The mystery man fails to phone the following month. Thumm and Lane open the envelope to find a simple notation: 3HS wM. At the museum, it is found a rare book was stolen from the display case and another book substituted. Thumm, Patience, and Lane seek to sort out the mystery consisting of several similar rare books and two similar people (Sedlar and Ales). Then one of them is found murdered, but which one is it? RM