The Ogre of Oglefort — Eva Ibbotson

For excitement-hungry orphan Ivo, a mission to save Princess Mirella from the dreaded Ogre of Oglefort is a dream come true. Together with a hag, a wizard, and a troll, Ivo sets out, ready for adventure. But when they get to the ogre's castle, the rescuers are in for a surprise: the princess doesn't need saving, but the depressed ogre does! It's a warmhearted, hilarious romp in the tradition of Roald Dahl, with enough creepy magic, ghosts, and laughs to make even the saddest ogre smile.