The Secret Garden by Frances Hodgson Burnett
After losing her parents and being shipped from India to the Yorkshire Moors, Mary Lennox is terribly lonely. Living in her uncle's gloomy mansion, she has nobody to play with. But one day, she learns of a secret garden somewhere in the grounds that her uncle won't allow anyone to enter. Then Mary uncovers an old key in a flowerbed - and a gust of magic leads her to the hidden door. Slowly, she turns the key and enters a world she could never have imagined...