The Secret of Platform 13

Under Platform 13 at Kings Cross Station there is a secret door that leads to a magical island.
It appears only once every nine years. And when it opens, four mysterious figures step into the streets of London. A wizard, an ogre, a fey, and a young hag 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.