Charlie Drake is a crack locksmith, so good that he once was called to open a stuck lock at the Tower of London. At the beginning of this film, Charlie is persuaded by a con man into opening a locked car and safe, winding up in jail for a year. When he gets out, he's tricked into opening some more locks, and gets three years. Drake now has an unwanted reputation as the top safe-cracker around. He wants to get out of the business when he's released again, but finds himself a pawn between two rival gangs. The gangs get together to steal the Stamford Collection of Fine Gems, but Drake and undercover policewoman Porter trip up the crooks and bring them to justice.