November 1924. The Endeavour sets sail for New York, with 2,000 passengers - and a killer - on board. When a body is found on deck, ship's officer Timothy Birch is ready to declare the death a tragic accident. But Scotland Yard inspector James Temple is certain there's more to this misfortune than meets the eye. Mounting an investigation, the pair uncover the theft of a priceless painting, and encounter a string of suspects with secrets to hide. Now, with just days remaining until the Endeavour reaches New York, their search for the culprit is fraught with danger. And all the while, the passengers roam the ship with a killer in their midst...