A couple makes the mistake of trusting their child to the wrong babysitter.

Bunny's parents should not have brought her to New York City, but her father has an important speech to make in the city, and her mother couldn't bear to be away from the darling nine-year-old girl. When Mommy and Daddy leave for the speech, Bunny will stay in the hotel with a babysitter, sound asleep and perfectly safe. What could possibly go wrong? The sitter is Nell, a plain young woman from Indiana whose dull expression conceals madness. She puts Bunny to bed and amuses herself in the other room, making prank calls and trying on the mother's jewelry. So far all is well, but something is broken inside Nell's mind. As long she is in charge, the child will not be safe.