Edgar Wallace 
Dark Eyes Of London [PDF ebook] 

Inspector Holt is enjoying the Caf 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 – including romance.