Dick Martin is leaving Scotland Yard. His final job, investigating a stolen book, takes him from a conversation with librarian Sybil Lansdown to a meeting with a Doctor Stalletti, who will become a key figure. Along the way, Martin becomes involved with a small-time crook—an expert at picking locks—who tells him about a recent lock-picking job that has made him quite nervous. But before he can pass along details, the lock-picker is murdered.

Next, the retiring detective gets involved in a couple of seemingly unrelated incidents—the theft of an obscure book, and an assignment to chase after a very rich and very elusive young heir who is rarely seen. In the midst of all the chasing about, there is a desperate search underway for seven individual keys which, when all used together, can open a mysterious door in a family's tomb.

Doctor Stalletti is involved, clearly an unsympathetic and sinister character, suspected of carrying out unethical medical experiments, to say the least. There are glimpses of some powerful and dangerous creatures who may or may not be linked to the doctor. In addition, we'll hear of librarian Lansdown's unfortunate habit of getting herself into dangerous situations.