One night in 1931 William Wallace was handed a phone message at his chess club from a Mr Qualtrough, asking him to meet at an address to discuss some work. Wallace caught a tram from the home he shared with his wife, Julia, to the address which turned out, after Wallace had consulted passers-by and even a policeman, to not exist.

On returning home two hours later he found his wife beaten to death in the parlour. The elaborate nature of his alibi pointed to Wallace as the culprit. He was arrested and tried, found guilty of murder and sentenced to hang, but the next month the Court of Criminal Appeal sensationally overturned the verdict and he walked free. The killer was never found.

Fifteen years on, the inspector who worked the case is considering it once more. Speculation continues to be rife over the true killer's identity. James Agate in his diary called it 'the perfect murder', Raymond Chandler said 'The case is unbeatable. It will always be unbeatable'. And on a cruise in 1947, new information is about to come to light.