Philippa Pearce

Tom Long is forced to stay with his Aunt and Uncle while his brother recovers from a bout of the measles. At their flat, he is disappointed to find there is no garden to play in; but his disappointment turns to wonder when he discovers a magical garden which only appears at night when an old clock strikes thirteen. (imdb)

Tom Long is staying with his Uncle and Aunt. When their grandfather clock strikes thirteen, Tom makes a strange discovery - a portal to the past where only a friendly girl called Hatty can see him. Adapted from a novel by Philippa Pearce. (imdb)