November 1924.

The ocean liner Endeavor sails from Southampton to New York and, in addition to the crew, there are two thousand passengers on board.

When the body of an elderly man is found at the bottom of the stairs, ship's officer Timothy Birch dismisses his death as a tragic accident. However, James Temple, a tough inspector from Scotland Yard, is sure that someone helped the apparent accident.

Birch agrees to help Temple investigate, and the trail quickly leads them to the theft of an extremely valuable painting that only the owner knew existed… and that dead man.

With only a few days left until landing in New York, Temple's very presence on board the ship is becoming increasingly suspicious, and Birch's search for the perpetrator is fraught with danger. Meanwhile, the passengers continue to walk around the decks and the killer is waiting somewhere among them...