Mandy Garland (Mandy Miller) is born without auditory nerves. Her parents, Harry (Terence Morgan) and Christine, aka Kit (Phillis Calvert), and her grandparents (Godfrey Tearle and Marjorie Fielding) keep her sheltered from the world, and by age six she's desperately lonely and doesn't know any language, despite efforts to teach her fingerspelling. Kit enrolls her in the Bishop David School for the Deaf, which focuses on teaching kids to speak. Headmaster Dick Searle (Jack Hawkins), new teacher Miss Crocker (Patricia Plunkett), and deaf founder Jane Ellis (Nancy Price) work to teach Mandy, but Harry disapproves of Kit's decision to place her in the school and fights to get her taken back out. Obstructive Bureaucrat Ackland (Edward Chapman) takes advantage of the minor scandal to try to steal Searle's job.
Mandy contains examples of:
- Baby's First Words: Mandy finally learns to say "mummy."
- Boarding School: The Bishop David school is normally this, but Mandy adjusts so badly to campus life that Searle takes advantage of a loophole to let her live in a nearby apartment with Kit.
- Character Narrator: Kit narrates the first few scenes.
- First Friend: An unnamed deaf girl is the first child to show kindness to Mandy, giving her a necklace made out of clay and later waving to her in the dorm at night.
- Forgot the Disability: Ellis sometimes has to remind people to look at her when they talk to her.
- Impairment Shot: Shots from Mandy's perspective are silent.
- Kids Are Cruel: Almost every interaction Mandy has with hearing kids is unpleasant. At one point, a boy takes her ball and won't give it back until she says "please." When she can't, he plays piggie in the middle with his friend, taunting her with it, until she attacks him and pulls his hair.
- Licked by the Dog: Searle's bluntness often causes adults to dislike him, but he's good with deaf kids. When he meets Mandy and her parents at a restaurant, Mandy runs into his arms.
- Meaningful Name: As Kit says in the first scene, "Amanda is Latin for 'one who deserves to be loved.' I don't know about deserving love. She certainly gets it."
- A Minor Kidroduction: The movie opens with Mandy as a two-year-old, when her parents realize she's deaf.
- Reading Lips: This is a major part of Mandy's education. By the end, she's gotten good enough to have a conversation with a boy with hearing.
- Too Unhappy to Be Hungry: The morning after Mandy arrives at school, she misses Kit so badly that instead of eating, she just stares into her cereal, then angrily shoves it away.
- While You Were in Diapers: Ackland tells Searle, "I was working for this school when you were still a boy!"