Even before Orion's departure, certain people on Earth were voicing their uneasiness about it. Of course, that was only a minor irritant to Ice and Brain as they were busy outfitting the Alpha Centauri expedition. Unfortunately, by the time the Expedition returned, the situation had gotten worse and had to be dealt with. Meanwhile, discoveries made on Mars, start a panic on Earth.

Between departure and return, the Scientists and crew of Orion brave the considerable dangers of Halcyon, only planet of Alpha Centauri. While searching for clues to the whereabouts of the Atlanteans and trying to keep their hides intact, they wonder . . . How did those Prehistoric Appetites get there, anyway?