As the train chugged along the tracks, English tourist Iris Henderson (Cybill Shepherd), still grappling with her recent adventures in the mystical land of Bandrika, found herself en route back home to prepare for her wedding. However, fate intervened when a sudden avalanche blocked the railway line, leaving the passengers stranded at a quaint hotel. Among this peculiar assembly were Charters and Caldicott, two passionate cricket fans eager to catch the final moments of a Manchester Test match, and Miss Froy, a governess concealing a remarkable musical talent.
As night fell, Iris's peace was disrupted by an inexplicable noise from the room above hers. It turned out to be Gilbert Redman (Elliott Gould), an ethnomusicologist whose clarinet playing captivated local folk dancers. Iris's attempts to have him removed were met with defiance, leading to a confrontation that left her feeling disquieted.
The following morning at the railway station, Iris's woes escalated when she was unexpectedly struck on the head by a planter plummeting from above. Thankfully, Miss Froy, always quick on her feet, assisted Iris onto the train, joining Charters and Caldicott as well as Eric Todhunter, a lawyer accompanied by his enigmatic mistress, who was masquerading as "Mrs. Todhunter." As Iris gradually regained her senses, she found herself sharing a compartment with Miss Froy and an assortment of strangers.
As the train continued its journey, Iris accompanied Miss Froy to the dining car for a calming cup of tea. However, their moment of tranquility was short-lived; upon returning to their compartment, they discovered that Miss Froy had mysteriously disappeared. The other passengers and even some train staff appeared intent on denying any knowledge of her whereabouts. Todhunter feigned ignorance, desperate to keep his illicit relationship a secret.
In a frantic search for her vanished friend, Iris sought Gilbert's help. Meanwhile, Dr. Hartz (played by Herbert Lom (/actor/herbert-lom)), a respected brain surgeon, suggested that her concussion might be playing tricks on her mind. Yet, as the train journeyed on, Charters and Caldicott insisted they had never encountered Miss Froy, masking their desire to avoid involvement in the mystery surrounding her disappearance with their fixation on the cricket match.
The situation grew even more convoluted as Todhunter's mistress, filled with ire over her lover's reluctance to finalize their divorce, confided having seen a shadowy figure that she believed was Miss Froy. Their first stop on this winding path of deception presented a patient of Dr. Hartz, concealed in bandages, accompanied by a mysterious nun who appeared to be deaf-mute. But just as Todhunter’s mistress was about to divulge crucial information, Madame Kummer appeared—a doppelgänger of Miss Froy—claiming she had played a vital role in Iris's recovery after her head injury. Fearing repercussions, Todhunter’s mistress attributed Madame Kummer to the woman she previously glimpsed.
As Iris and Gilbert pressed on in their quest for Miss Froy, they stumbled upon her glasses tucked away in the baggage car. However, their pursuit was soon interrupted by Signor Doppo, a clever magician secretly hiding in Iris's compartment. In the ensuing tussle, they lost her glasses and Doppo managed to escape. Iris's keen observations led them to realize that the nun accompanying Dr. Hartz's patient was wearing high heels, igniting suspicion that the patient could, in fact, be Miss Froy herself.
Over shared drinks in the dining car, Dr. Hartz confessed to being part of the conspiracy, revealing that the passengers had been drugged. Yet, it was soon clear that the false nun, actually a British woman in disguise, acted out of solidarity to her countrymen. With newfound clarity, Iris and Gilbert successfully plotted an escape, liberating Miss Froy from her captors and cleverly substituting her with Madame Kummer.
As the train neared the border, Dr. Hartz uncovered their ruse. He redirected part of the train onto a branch line, where soldiers awaited. Gilbert and Iris alerted their fellow passengers about the unfolding chaos. A soldier boarded the train, commanding everyone to comply. Undeterred, Gilbert and Iris overpowered the soldier and seized his weapon. Just as it seemed they had gained control, another soldier opened fire, injuring Charters.
Once the tumultuous gunfight quieted down, Miss Froy revealed her true identity as a spy to Gilbert and Iris and hastily took off into the surrounding forest. In a surprising twist, she bestowed upon them an encoded message brilliantly woven into a melodic tune they were tasked to deliver to the esteemed Foreign Office in Whitehall—the same melody performed moments prior by a murdered street musician. With her fate hanging in the balance and gunfire echoing all around, Todhunter made a futile attempt at surrender, ultimately meeting a grim end.
Onboard, Gilbert and Caldicott took command of the train while the unconscious soldier awoke with malicious intent, posing a threat to all remaining passengers. The enigmatic nun, who had cleverly disguised herself, made an audacious escape through a side door, switching the tracks before being shot in the leg. Nevertheless, Caldicott and Gilbert managed to pull her to safety.
As Charters and Caldicott arrived in London, they were met with the news that the much-anticipated Test Match had been abruptly canceled due to unforeseen flooding. Amidst the upheaval, Iris found herself at a distance from her fiancé, leading her to make the impulsive choice to share a taxi ride with Gilbert, resulting in an unexpected first kiss.
Finally, upon reaching the Foreign Office, Gilbert's composure wavered as he struggled to recall the pivotal tune entrusted to him. While awaiting their turn in the reception area, the delightful sound of Miss Froy playing the melody on a grand piano suddenly filled the room, instantly igniting recognition as the doors swung open to unveil her glorious return.
