RJ Spencer is a lucky 12 year old. He lives in the big city and his parents are landlords of the high-rise apartment building that is his home.

The many tenants in the building, along with the endless possibilities of adventures in the city itself, are the perfect setting for the young detective as he sets out to solve every case he can get his hands on.

In this mystery, RJ and his younger pal Joey come upon Mr. Porter, the new tenant in 3B, while he is trying to maneuver a very large crate into his apartment. What is inside the mysterious box, and will RJ and Joey solve the mystery without blowing their cover?