Mary is sent to live with her uncle in a large house called Misselthwaite Manor after her parents and servants all die of cholera. Mary is quite upset about this.
The servants here are strange and more aloof than those back home. There's also nothing to do here but go outside and play with sticks and stones. This angers and bores young Mary.
Mary begins to spend her time searching for the key. She has spent so much time outside now that she has begun to look less sickly and frail than she used to.
Mary hears about one of the gardens in Misselthwaite. Mr. Craven had locked it up for ten years and buried the key. This instantly intrigues Mary. It's the perfect thing to occupy her here!
Mary finds the key to the garden and unlocks it. She has found her way inside the "Secret Garden" of Misselthwaite! Overjoyed, Mary decides to make plans to bring it back to life with gardening. To do that, she'll need help.
Mary finds a boy named Dickon, her servant's brother. She takes Dickon to the "secret garden" and they spend all day there, fixing it up. Mary is extremely happy with the garden and spends more and more of her time there, but she never tells anyone other than Dickon. She wants it to stay a secret.
The secretive nature of the garden is almost ruined when curiosity leads Mary to a boy named Colin. Colin is a sickly, spoiled boy who wants to see the garden at any cost. This means making the staff aware of the garden being opened! Mary manages to convince the boy to keep it a secret.