The Wheel Spins (Aka The Lady Vanishes)

"Adept at laying one icy finger on the back of your neck" Spectator

Iris Carr, a beautiful, young socialite on her way back home on a train to England after vacationing in the mountains of central Europe. Afraid while travelling alone, she befriends Miss Froy, who suddenly disappears without a trace. No one on the train believes that Miss Foy is missing and what's more they don't see to believe that she even existed.

A 'Girl on a Train' meets a 'Locked room' mystery, Ethel Lina White's The Wheel Spins was first published in 1936. It was adapted by Sidney Gilliat and Frank Launder and then filmed three times, most notably by Alfred Hitchcock as The Lady Vanishes (1938).