Philippa Pearce's novel, Tom's Midnight Garden won the prestigious Carnegie Medal in 1958 and has been dramatised a number of times (more on that shortly).
When Tom Long's younger brother, Peter, gets measles (back in the days before all children were automatically immunised against this illness), Tom is sent to stay with his aunt and uncle in their small flat which has no garden. Since Tom may be infectious, he's not allowed to go out and, lacking exercise and eating more than usual (thanks to the rich diet his aunt is supplying), Tom is not sleeping at night. The only thing that interests Tom is the strange grandfather clock in the hall of the big house which has been divided into flats. The clock seems to have its own ideas about time, especially after midnight when it's in the habit of striking thirteen! Finding himself compelled to investigate, Tom slips out of the back door, whilst his aunt and uncle sleep, and finds himself in an astonishing garden that's in full bloom, instead of in the expected back yard containing dustbins and a car under a tarpaulin.
Tom explores the garden, rather nervously at first and discovers that four children live in the house with this magnificent garden: three are boys and one is a girl. Unfortunately for Tom, who would have liked to play with James, only the boys' cousin, Hatty, seems able to see him - and she believes he's a ghost. In fact, Tom does behave rather like a ghost - he's able to walk through walls and doors, and he leaves no footprints. But the pair make friend and have plays some wonderful, absorbing games, climbing trees and hiding in special places. Only Abel, the gardener, seems to pay any attention to Hatty's strange, solitary games, and if he can see anything at all he says nothing about it, merely hanging on to his Bible.
However, something strange happens to Time, even in this fantastic garden, because although Tom goes to play with Hatty every night during his stay with his aunt and uncle, she seems to be growing up fast. And as Hatty grows up, Tom seems to her to be growing fainter. They manage to share one last adventure before Tom has to go back to his parents and brother, and the start of the new school year. This adventure involves a pair of skating boots, a secret hiding place, and the two children wearing the same pair of skates at the same time.
This is a terrific story and I can quite see why it's become a classic of children's literature. It's been dramatised on a number of occasions: the BBC produced a full-cast dramatisation audiobook, as well as filming it as a mini-series more than once. There's also a full-length movie. I shall have a look for the movie or one of the mini-series in a few months time (once the images from the book are out of my head and I can do the visual dramatisation justice).