A certain woman had been certified as insane, but owing to a blunder the ambulance went to the wrong house and forcibly took away an Englishwoman, who did not understand a word of the language, or of her destination. In her indignation and horror at finding herself in a private asylum, she became so vehement and violent that she was kept at first, under the influence of drugs.
When the mistake was found out, the doctor - who was a most unscrupulous character, was afraid to admit it. At the time he was in financial difficulties, and he feared it might ruin his reputation. So he planned to detain the Englishwoman until he could release her as officially cured.
"But she couldn't know she wasn't in for life," explained Miss Froy, working up the agony. "The horror of it would probably have driven her really insane, only a nurse exposed the doctor's plot, out of revenge...But can you imagine the awful position of that poor Englishwoman? Trapped, with no one to make inquiries about her, or even to know she had disappeared, for she was merely a friendless foreigner, staying a night here and night there, at some Pension. She didn't understand a word - she couldn't really explain - "
"Please stop," broke in Iris. "I can imagine it all. Vividly...."
The book has a wonderful cast of supporting characters - the professor, his young acquaintance, the honeymooning couple, the parson and his wife, the baroness, the blonde beauty...all have a role to play in this journey.
I love mysteries set in trains and this - with its frantic rhythm - was most enjoyable.
First Line: The day before the disaster, Iris Carr had her first premonition of danger.
Title: The Wheel Spins (The Lady Vanishes)
Author: Ethel Lina White
Publication Details: NY: ibooks, 2004
First Published: 1936
Trivia: The book was made into a movie by Alfred Hitchcock in
Being out of print, the book is not so easily available. Nitu didi borrowed and brought it for me from Mississauga Library System. 
Book(s) with similar theme(s)
Murder on the Orient Express
Mystery and Suspense