Some time before Buck Roger's arrival, Col. Wilma Deering had set out to capture two interstellar gun runners. A fire in their spacecraft left them disfigured and they now set out to take their revenge on Wilma and Earth. Capturing a freighter with 20th Century chemical weapons, they plan to poison the planet's atmosphere. With the aid of retired members of the Earth Defense Directorate's 69th Squadron, Buck and Wilma attack the gun runners' base to destroy them and the chemical weapons.

To discover the secret behind a terrifying riddle presented to him, Buck subjects himself to a mind probe in an attempt to find out who is responsible for the mysterious objects being transported into the Defense Directorate's building.