The Secret of Platform 13

Under Platform 13 at King's Cross Station there is a secret door that leads to a magical island. It appears only once every nine years. When it opens, four mysterious figures step into the streets of London: a wizard, an ogre, a fey and a young hag, who have come to find the prince of their kingdom, stolen as a baby nine years before. But the prince has become a horrible rich boy called Raymond Trottle, who doesn't understand magic and is determined not to be rescued.

Endorsements

"This kind of fun will never fail to delight" — Philip Pullman