November 1907. George Dillman and Genevieve Masefield sail from Liverpool to New York on the maiden voyage of the luxurious Mauretania. Employed by the Cunard Line again as private detectives, they pose as passengers on what proves to be a very eventful crossing.

Dillman is instrumental in rescuing a crew member from being washed overboard in severe weather, but he is unable to save one of the first-class passengers from the same fate. At first, it looks like a case of death by misadventure, but is the presence of a record shipment of gold bullion on board just too great a coincidence? Dillman and Genevieve must fathom the motive for murder before it is too late.