The Door with Seven Locks

Retiring detective Dick Martin takes what looks like an easy job guarding a rare book and instead stumbles into the affairs of the Selford family, whose ancestral tomb is sealed behind a door with seven separate locks. Seven keys were scattered so that no single person could open it, and someone is now collecting them by any means at hand. Wallace crowds the story with a sinister experimenting doctor, a hulking manservant, a quick-witted librarian named Sybil Lansdown, and a hidden fortune men will kill for. It moves at the cliff-edge pace that made him the most-read thriller writer of the 1920s. Free to download here as a PDF and EPUB edition.