The body of Anton Zoref is invaded by an unknown life force. The man soon manifests an uncontrollable ability to absorb energy. As the Alphans struggle to understand this mysterious force, Zoref's need becomes insatiable. Driven by instinct, he makes his way to the greatest source of energy on Alpha: the Nuclear Generating Plant.

After an encounter with a space-time anomaly, the Alphans find their Moon back in the Solar System on a course to re-enter Earth orbit. The celebration ends when it becomes apparent Earth is an inhospitable wasteland. The mystery deepens when they discover a duplicate Moon already in orbit and a duplicate Moonbase Alpha lying empty and deserted.

The Alphans are visited by a bizarre spacecraft, whose request for supplies hides a deeper purpose. The ship, Gwent, is found to be sentient, the attempt of a vain alien genius to live forever. Powerful, unstable and craving companionship, Gwent intends for Koenig, Helena and Bergman to replace its aged, dying creator.

The wandering Moon suddenly changes course and comes to a halt in the vicinity of a dead world. As Alpha's power fails, the only hope for survival is to evacuate to the planet, which was ravaged by a nuclear war in the distant past. Searching for answers, a team is sent to the surface, where they discover the shocking truth of the origin of Mankind.