Fred was a security guard watching over a valuable diamond on display. He decided to take a tea break while three other people - an elderly man, a well-dressed woman, and a scruffy young man - were viewing the diamond. When Fred returned, the diamond had been stolen. Detective Finder is called in to investigate. He finds evidence that the security system was tampered with by an expert. Fingerprints at the scene include those of Fred and the three viewers. Two sets of prints are unknown.