Tom is sent away to stay with his aunt and uncle for the summer holidays. With no garden or children to play with, he feels lonely and unhappy, until one night he hears the clock striking thirteen and discovers a secret garden where he makes a new friend, Hatty. Yet it soon becomes clear that his new-found friend is living in another time altogether, and to her, Tom is a sort of ghost. Each time he visits the garden, Hatty has grown older. Finally, on a skating trip up the frozen river in the garden, Hatty and Tom begin to fade and become invisible to each other once more.