Recently released from prison, Arthur Payne meets a benevolent stranger on a train who says he may be able to help him. A few days later, a second stranger arrives at Payne's houseboat, and Payne reluctantly agrees to carry out a no-risk jewel theft for a fee. When the staged burglary turns to murder, Payne realises he's been set up and he goes on the run. All the evidence points towards Payne being the murderer, but one irrefutable fact troubles Inspector Jackson.