The Secret of Platform 13

The Secret of Platform 13 is a children's novel by Eva Ibbotson, illustrated by Sue Porter and first published in 1994. It has drawn attention for its resemblance to the Harry Potter books, and its own hidden door is not a platform for a train but a gump, an opening behind platform 13 of King's Cross station that appears once every nine years and stays open for nine days.

The gump leads to the Island, a paradise inhabited by giants, mermaids, water nymphs, wizards, witches, hags and merrows. Shortly before it last opened, the Queen gave birth to a son, and his three nurses asked to visit London while they had the chance. On the ninth day, while one of them sat outside a fish and chip shop with the baby, a woman called Mrs Trottle, who was desperate for a child, drove away with him and left a china doll in his place.

Nine years later the opening comes round again, and the Island sends a rescue party made up of a young hag named Odge Gribble, an old wizard, a gentle fey and a giant ogre. Their task is to find a prince who has grown up in London as somebody else's son and bring him home, and the gump gives them nine days in which to do it.