On a journey home from the fictional country of Bandrika, Iris Henderson, an English tourist, plans to marry soon and return to normal life. Her escape route is suddenly interrupted when an avalanche blocks the railway line, forcing stranded travelers to spend an uneasy night at a local hotel. Among the company are two cricket-obsessed friends, Charters and Caldicott, who are eager to witness the final days of a Test match in Manchester, and Miss Froy, a governess and music teacher whose calm presence contrasts with the growing tension around them. That same evening, a street performance ends in tragedy as the folk singer is murdered by an unseen assailant, sending a shiver through the carriage-turned-inn.
Earlier, Iris endures a disturbance from the room above hers—a loud, persistent noise from a tenant named Gilbert Redman, an ethnomusicologist who plays the clarinet for local folk dancers. Iris tries to have him moved, but he confronts her, and the confrontation ends without a resolution that night. The next morning, Miss Froy accidentally drops her glasses near Iris and her companions, and when Iris tries to return them, a planter from above falls and knocks her unconscious. Miss Froy helps her onto the train, and Iris, still dazed, waves goodbye to the others before fainting.
When Iris comes to, she finds herself in a compartment with Miss Froy and several strangers, including Charters and Caldicott, Gilbert, and the lawyer Eric Todhunter with his mistress, who is posing as “Mrs. Todhunter.” Iris joins Miss Froy in the dining car for tea, and Miss Froy gives the waiter a package of her favorite tea and explains that she only drinks this particular brand. Shortly after, Iris falls asleep and awakens to discover Miss Froy has vanished. The other passengers deny ever having seen her, and Todhunter pretends not to remember her in order to avoid drawing attention to his liaison with his mistress. Gilbert agrees to help Iris search for Miss Froy, while brain surgeon Dr. Hartz suggests Iris may be experiencing “concussion-related hallucinations.” Fearing they will miss the cricket match, Charters and Caldicott also claim not to remember Miss Froy.
Tensions mount as Todhunter’s mistress reveals she did see Miss Froy, and later a peculiar sequence unfolds: Dr. Hartz’s patient, whose head is completely bandaged, is brought aboard on a stretcher accompanied by a nun who appears to be deaf-mute. A woman dressed exactly like Miss Froy, Madame Kummer, appears and claims to have helped Iris after she was struck on the head. Todhunter’s mistress says she saw Madame Kummer, though Iris briefly doubts her own memory. In a landmark moment, Iris recalls sharing tea with Miss Froy and notices where Miss Froy wrote her name on a window. She pulls the emergency brake and faints again.
Gilbert grows convinced Iris is not hallucinating when a tea package wrapper briefly sticks to a corridor window, revealing the special brand Miss Froy favored. The pair continue their search and eventually locate Miss Froy’s glasses in the baggage car, only to be attacked by Signor Doppo, a magician who had been in Iris’s compartment. They lose the glasses in the struggle, and Doppo escapes.
Iris and Gilbert deduce that the nun accompanying Dr. Hartz’s patient is wearing high heels, hinting that the patient has been replaced by Miss Froy. Dr. Hartz leads them to the dining cars for a drink and then back to a compartment, where he admits the patient is indeed Miss Froy and that he is involved in a conspiracy—and that they have been drugged. The false nun, revealed to be a British woman in disguise, did not drug them out of loyalty to her countrymen.
Gilbert and Iris escape, free Miss Froy, and swap the impersonator back for Miss Froy. As the train nears the border, Dr. Hartz discovers the plan and diverts part of the train onto a branch line where soldiers lie in wait. Gilbert and Iris alert the other passengers to the danger, and a soldier boards with a pistol. They knock him out, but another soldier fires and wounds Charters in the hand. A tense gunfight ensues. Miss Froy discloses that she must flee because she is actually a British spy and hands them a coded message (encoded in a tune) for the Foreign Office in Whitehall—the same melody the street musician performed earlier. Miss Froy runs into the forest, and the fate of the others on the train remains uncertain.
Todhunk—sorry, Todhunter—tries to surrender, waving a white handkerchief, but is shot dead. Gilbert and Caldicott commandeer the locomotive, and the knocked-out soldier regains consciousness and threatens the group. The false nun escapes through a side door and switches the tracks, but Gilbert and Caldicott manage to pull her back aboard just in time.
Back in London, Charters and Caldicott learn the Test Match has been canceled due to flooding. Iris, who has reunited with Gilbert, sees her fiancé from afar at the station and hails a cab with him, sharing a kiss as they head toward the Foreign Office. In a tense sequence, Gilbert realizes he cannot remember the vital tune, but as they are led into the Foreign Office, the familiar melody rises from a piano—Miss Froy is indeed safe, and the encoded message will reach its destination.
The long ride, the multiple layers of deception, and the peril on board ultimately resolve into a quiet, dramatic restoration of truth: Miss Froy’s mission remains intact, the conspirators are brought to light, and Iris and Gilbert’s bond strengthens as they step into a future where the tune’s secret message becomes a bridge to certainty.
The cast includes Kathleen Fee, Florence Desalme, and Jeannie Walker in key voice roles. Kathleen Fee, Florence Desalme, and Jeannie Walker appear in these capacities, contributing to the film’s multilingual presentation.
