Based on Frances Hodgson Burnett's novel, an orphan girl helps a rich boy who has been crippled by his father's grief.
In India two British officers find Mary Lennox (Margaret O'Brien) after her parents died of cholera. Mary returns to England and says her uncle is rich. Mrs. Medlock (Gladys Cooper) picks her up at the dock, takes her in a coach to a large house, and tells her to stay in her room. The servant Martha (Elsa Lanchester) laughs, and Mary cries. Mary refuses to eat porridge and walks in the garden. Dickon (Brian Roper) tells her about a secret garden.
Mary hears someone crying in the house. Mr. Pitcher (Dennis Hoey) takes Mary to her uncle, Archibald Craven (Herbert Marshall), who says he is going to London for a long time. He says his wife died ten years ago, and he keeps to himself.
Mary meets the gardener Ben Weatherstaff (Reginald Owen). She talks to a raven and finds a key. At night Mary finds Archibald's son Colin Craven (Dean Stockwell) in his room. He says his legs are crippled. Colin says his mother was killed by a tree. Mary says she hates her dead mother too.
Mary shows Dickon the key. They find the gate and see that the garden has been neglected for ten years. They find the limb that killed Archibald's wife. Mary tells Colin about India. When he quarrels with her, Mrs. Medlock sends Mary out. Dr. Griddlestone (Aubrey Mather) checks the irons on Colin's legs.
Mary takes a daffodil from the garden. Colin is screaming, and the servants scurry. Mary yells back at him as the servants watch. Colin asks her to tell him a story. Mary brings Dickon and animals to Colin, who promises not to tell their secret. The raven scares Dr. Griddlestone away. Dr. Fortescue (George Zucco) tells Dr. Griddlestone to take off the irons, and he prescribes exercise. Dr. Griddlestone refuses.
Mary and Dickon take Colin in a wheelchair to the garden. Outside the gate he tries to walk but falls. The garden is blooming colorfully, and Colin says he will live forever. Archibald complains to Dr. Fortescue about his report. Dr. Fortescue suggests that Archibald has transferred his desire to die to his son.
Ben finds Mary, Dickon, and Colin in the garden and makes them leave. At night Dickon tells Colin and Mary that Ben saw the accident in the garden. Archibald tried to chop down the tree but couldn't. David and Mary hide before Archibald comes in. Archibald tells Colin he is taking him to Italy and will sell the house. Colin says not to sell it.
Mr. Bromley (Matthew Boulton) writes a check for Archibald and says the garden is beautiful. Archibald goes to the garden, and Colin walks. Archibald is happy and will stay.
This spiritual parable depicts how a man's excessive
grief can affect his son by his projecting onto him such a dismal
future that he makes no effort to live in a healthy way. However,
playing with other children helps him to realize the joy of living.