The Door with Seven Locks (1926) - Edgar Wallace

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.