Boggart, Book 1: The Boggart

The Volnik family has just inherited a castle in Scotland, so they take a trip to see the relic and then decide to head back home with a few choice antiques. One of those antiques is a locked roll-top desk that contains, unbeknown to the Volniks, a "boggart." Unlock the desk, and the invisible boggart is free ... free to do whatever he pleases. Great pranks ensue. Fun and funny! The sequel to this book is The Boggart and the Monster.