Here's the so-far untitled synopsis (title suggestions welcome):
Abby and Eliza’s dad has a new girlfriend, Susan. They hate her, of course. But when Susan invites them all to go on vacation to her family’s summerhouse in Cape Cod they can’t resist their first airplane trip and adventure to the east coast. Once they get to the old saltbox house on the Cape, strange things start to happen. Abby has visions of someone who lived in the house long ago. Drawings appear in her sketchbook, as if done by her hand. Abby's mysterious experience at the cemetery scares her, but she’d rather chase ghosts than spend time with Susan. The town's historical society reveals surprising things about Susan’s house and what went on there centuries ago. But Abby is not surprised, her dreams have been telling her about these events. When Abby tries to tell Dad what she’s experiencing, he doesn’t believe her. But Susan does, because Abby’s visions sound all to familiar to her. Together she and Abby work to solve the mystery, becoming closer in the proces to each other and to a girl from the past who needs their help.