This book is mainly about a wayward and lonely rich girl, Mary, who became an orphan due to a sudden plague and was sent to a relative's house in an ancient manor in England for adoption. Among the secluded and quiet countryside and simple villagers, her temperament gradually became common. One night, following the faint cry from one end of the corridor of the mysterious mansion, she was brought to an equally strange and lonely little life. Colin, Mary's cousin and the young owner of the mansion, was born weak and ill in bed for many years. His temperament was unpredictable. To help Colin, Mary took him into the secret garden of the manor, which had been closed for many years. The children played undisturbed in the vibrant small world, learned to be friendly to others, and restored their pure and happy nature.