A professor comes up with a system to win at roulette and goes to the famous casino at Monte Carlo to try it out. When he turns up murdered and his “system” missing, a reporter sets out to find the killer–and the system.

A Fleet Street reporter (Errol Flynn) investigates mathematics professor Dr Becker’s claim to have a foolproof system for winning at roulette in Monte-Carlo. He refuses to take his fiancée Gilian (Eve Gray) along, but she decides to go anyway and report on the story for a rival newspaper. Dr Becker eventually dies and it looks like suicide, but Gilian is convinced it was murder. The end goal is for Gilian to get all the suspects in the same room and reconstruct the crime.