When a desperate passenger is found murdered on an overnight ferry, Chief Superintendent Henry Tibbett and his wife Emmy find themselves trapped in a high-stakes investigation among their fellow travelers. The Tibbetts must navigate a complex web of international intrigue after discovering that the victim was carrying stolen diamonds and that their own belongings have been compromised. As the couple attempts to identify the killer among the passengers who shared their lounge, they are drawn into a dangerous conspiracy that threatens their safety. The narrative follows a traditional mystery structure, utilizing a third-person perspective to track the movements and motives of the suspects aboard the ship.

This work is characteristic of the classic British detective novel, emphasizing logical deduction and the interplay between a seasoned investigator and his observant spouse. The premise suggests a focus on the mechanics of the whodunit, utilizing the claustrophobic environment of the ferry to heighten the sense of urgency. Readers often appreciate the balance between the procedural elements of the Scotland Yard investigation and the personal stakes introduced by the Tibbetts' involvement. The narrative structure points to a methodical unraveling of clues, typical of the genre's mid-century golden age revival style.