Charly Gordon (Cliff Robertson), who has an IQ of 69, is constantly derided by his boss and fellow employees at the bakery where he works. His efforts to read and write prove fruitless. But when Dr. Straus (Lilia Skala) offers Charly an opportunity to participate in a radical medical experiment, he becomes a certified genius. The newly educated Charly develops feelings for his teacher, Alice Kinian (Claire Bloom), but their happiness is threatened by an unforeseen complication.