Wait till Helen comes

de Mary Downing Hahn

Molly and Michael dislike their spooky new stepsister Heather, but realize that they must try to save her when she seems ready to follow a ghost child to her doom. Heather likes to get her older stepbrother and stepsister into trouble. When the family moves to the country, Heather starts talking to a ghost named Helen. Heather's strange behavior concerns her siblings, but when Helen the ghost actually appears, concern diminishes into fear.