When their mom remarries, Molly and her brother, Michael, try to make friends with their new stepsister, Heather. But Heather only wants to make trouble for them. She lies and tattles and misbehaves, and somehow they always get the blame. They know she’s trying to drive a wedge between her father and their mother so she can have her father all to herself—and it seems to be working.

Then, Heather starts playing in the graveyard behind their new house. She claims she can talk to a ghost named Helen, and her behavior gets even stranger. Michael doesn't believe in ghosts and thinks their new little sister is just looking for more attention. But Molly isn't so certain, especially when Heather threatens that Helen is going to come for them and make them sorry.

It seems as though things can’t get any worse—but they do.

When Helen comes.