An unbalanced doctor and his brother murder a series of wealthy men to benefit from their life insurance policies, using a charity for the blind as a front for their activities.

Inspector Holt is enjoying the Cafe de la Paix and the Boulevard des Italiens. He and his valet Sunny are planning a visit to Monte Carlo when an urgent telegram arrives from the Chief Commissioner of Scotland Yard. Mr. Gordon Stuart has been found drowned in suspicious circumstances. Holt returns on the same boat as Flash Fred Grogan, continental crook and gambler. Attempting to solve the mystery leads Holt into a string of exciting adventures and romance.