When the children learn that an old library is to be torn down, they start cleaning it up, hoping that it will qualify for landmark status. But something strange is going on--they hear noises, and their lunch is stolen, and one day they arrive at the library to find the place has been ransacked. Who is trying to destroy their good work?

The Aldens help restore an old library by cleaning up and clearing out old books. But while they work, they hear mysterious footsteps on the second floor. Then someone sneaks in and makes the library just as messy as before. Why would someone want the library to stay closed?