A diverse group of passengers is stranded during a snowstorm at a remote inn in the fictional European country of Bandrika. Among them are Iris Henderson, a young British woman returning home for her wedding, and Miss Froy, a kindly governess. When the weather clears, the passengers board a train bound for England. Iris befriends Miss Froy, who later vanishes, seemingly without a trace. Disturbed by the sudden disappearance, Iris seeks help from another passenger, the charming musicologist Gilbert, to find Miss Froy.

Despite initial skepticism, Gilbert becomes convinced that Miss Froy's disappearance is suspicious. As they delve deeper, they encounter mysterious circumstances and uncooperative fellow passengers, leading to a series of thrilling twists and turns. The search becomes increasingly complex and perilous, drawing Iris and Gilbert into a web of intrigue involving espionage, deception, and danger. The tightly woven narrative builds up suspense as several characters' true motives come to light, setting the stage for a gripping and suspenseful confrontation.