Heir of Mystery by Philip Ardagh - USED

In this second Unlikely Exploit, Fergal McNally's brain--last seen in a pickling jar in the basement of Sacred Heart Hospital--is stolen, and the remaining McNally children find themselves mysteriously drawn to Fishbone Forest and the forgotten crumbling mansion that lies at its heart. There they meet the terrifying, teddy-bear-clutching Mr. Maggs, who has a fondness for riddles and is making big plans to change the world...which all sounds rather unlikely, doesn't it?