The Boggart: 08/22/13
The Boggart by Susan Cooper is about a mischievous magical creature who suddenly finds itself in Canada. After the death of the old Laird and his dog, the Volnik family — distant relatives — inherit the old Castle Keep.
The Boggart's main problem is ending up with a family who doesn't believe in magic. As the castle didn't come with instructions re magical beings, his pranks both at the castle and later in in the Volnik's home go unnoticed at first. Rather than stop (as that's not in its nature) he resorts to bigger and bigger pranks until they become dangerous!
Although the book is dated (especially in terms of the computer hardware that's central to the plot) it's still an enjoyable read. I listened to it on audio and found myself sucked right in.
There's a sequel called The Boggart and the Monster (1997).