Sam, Egg, Gum and Cat, and the other members of the Franklin Middle School Science Club are on a guided tour of Greater River City Air Force Base (otherwise known as Zone 99), an aspiring science museum, and Gum is convinced that if they can sneak away from the group they will find evidence of aliens--and it is up to the reader to choose how their adventure unfolds.

When Franklin Middle School's sixth grade class visits the River City Museum of Moving Pictures, Sam, Egg, Gum, and Cat discover three mysteries to investigate.