Build a movie plot around this: Who discovers the switch? Dr. Hartz
A:
Catherine Lacy, Margaret Lockwood and Michael Redgrave in The Lady VanishesEnglish tourist Iris Henderson (Margaret Lockwood) arrives at the "Gasthof Petrus" inn in the country of Bandrika, "one of Europe's few undiscovered corners". Iris is returning to Britain to marry a "blue-blooded cheque chaser", but an avalanche has blocked the railway line. The stranded passengers are forced to stay the night at the inn, including Charters and Caldicott, cricket enthusiasts who want to return to England to see the last days of the Test match.That evening, Iris complains about loud folk music coming from the room above her. She has the guilty musician, Gilbert Redman (Michael Redgrave), thrown out of his room, only to have him move into hers, forcing her to capitulate.Miss Froy (Dame May Whitty), a former governess and music teacher, listens to a tune performed by a folk singer under her window. Unseen by her, the singer is killed.The next morning, before catching the train, Iris is hit on the head by a planter apparently aimed at Miss Froy, who then helps Iris onto the train. Also on board are Charters and Caldicott, Gilbert, a lawyer named Todhunter and his mistress "Mrs. Todhunter". As a result of her injury, Iris blacks out. After the train is moving, Iris wakes up in a compartment with Miss Froy and several strangers. She joins Miss Froy in the dining car for tea. Unable to be heard above the train noise, the elderly lady writes her name on the window with her finger. Soon after, they return to their compartment, where Iris falls asleep.When Iris awakens, Miss Froy has vanished. The strangers in her compartment say they know nothing about an English lady. Even Todhunter in the next compartment, who spoke with Miss Froy earlier, pretends not to remember her. Iris searches, but cannot find her. She meets up with Gilbert, who agrees to help. Dr. Hartz (Paul Lukas), a brain surgeon, says Iris may be suffering from concussion-related hallucinations. Charters and Caldicott also claim not to remember Miss Froy,...