This book is the first in a series about Lewis Barnavelt, a very unlikely hero, and it's set in the late 1940s.
Lewis lives with his Uncle Jonathan in a very old house that contains lots of secrets. In this first book, Lewis discovers that Uncle Jonathan and his close friend Mrs. Zimmerman are witches, and he gets into trouble when he tries to perform some magic of his own, unwittingly resurrecting the evil Serenna Izard [sic].
Some other titles in the series are The Figure in the Shadows, The Letter, The Witch and the Ring, and The Ghost in the Mirror. These are exciting yet non-threatening Gothic-style mysteries written for 10-14 year-olds, and include a few illustrations by the well-known artist Edward Gorey.
Mary Lowe, 2001