Orphaned Mary Lennox (Margaret O'Brien) arrives at the Yorkshire mansion of her mysterious Uncle Craven (Herbert Marshall). Bitter and confused after the death of her parents, she clashes with the other residents of the estate, including the surly housekeeper (Gladys Cooper), the giggling maid (Elsa Lanchester) and Craven's invalid son (Dean Stockwell). After discovering a key to a secret garden, Mary seeks the means to heal herself and the other inhabitants of the Craven household.