I have read The Landlady by Roald Dahl and I have also seen the movie by Alfred Hitchcook. The movie and the short story both had unexpected endings. The novel and the movie were slightly different because in the short story the boy was 17 years old but in the the movie he was 22 years old.
It was very unexpected because Billy Weaver finds out the old landlady stuffed her dead animals and stuffed the other guest. He find out he is next one