While the Johanssens are away, Stacey's in charge of walking their dog, Carrot, and watching their house. At first, it's fun. Then strange things start to happen. Carrot behaves oddly, trash appears in the wastebasket Stacey emptied, and appliances she hasn't used feel warm. Soon she's really scared: she is sure someone else is in the house. Who could it be? And why are they are there? Stacey and the BSC are determined to find out --- before something really awful happens.