When Jessica comes to stay with her cousin James for the summer half term, they pass a creepy old house on their way to the town museum. James rescues Maddie Quedgley, a girl their age, from being run over by a speeding truck, but when James and Jessica, known as the Two Jays, insist on taking Maddie home, it is to a house where she seems to be living on her own. From down in the basement they hear footsteps walking around above them. When the door to the basement is suddenly locked, things become dangerous. Someone is very keen to get hold of a valuable item Maddie's father is guarding. So who is the man watching them in the museum, and who is the mysterious Ethan?
This is the fifth Two Jays adventure story. They can be read in any order, although each one moves forward slightly in time.