Charly Gordon is a gentle adult with the mind of a child. Determined to improve himself, he attends night school, where he soon earns the sympathy of his attractive teacher, Alice (Claire Bloom). When Charly's attempts at learning prove useless, he volunteers for experimental brain surgery, which accelerates his IQ to genius levels. However, with the treatment, he also encounters complex emotions for the first time in his life, such as love, and he falls for Alice. But a frightening discovery soon leads him to challenge everything he's been told.