When Tom Long's brother Peter gets measles, Tom is sent to stay with his Uncle Alan and Aunt Gwen in a flat with no garden and an elderly and reclusive landlady, Mrs Bartholomew, living upstairs. Because he may be infectious he is not allowed out to play, and feels lonely. Without exercise he is less sleepy at night and when he hears the communal grandfather clock strangely strike 13, he investigates and finds the small back yard is now a large sunlit garden. Here he meets another lonely child called Hatty, who seems to be the only one who can see him. They have adventures which he gradually realises are taking place in the 19th century. And each night when Tom visits, Hatty is a different age, chronologically out of sequence.
The book is regarded as classic, but it also has overtones that permeate other areas of Pearce's work. We remain in doubt for a while as to who exactly is the ghost; there are questions over the nature of time and reality; and we end up believing that the midnight garden is in fact a projection from the mind of an old lady. These time/space questions occur in other of her books, especially those dealing with ghosts. The final reconciliation between Tom, still a child, and the elderly Hatty is, many have argued, one of the most moving moments in children's fiction. I highly recommend it! :D