The sensors of the Moonbase Alpha, which wanders aimlessly through space with nearly 300 crewmembers, announce that a spaceship of unknown origin nears...

As an alien spaceship fast approaches, Koenig takes no chances and sends out two Eagles to intercept and gather more data. But when the Eagles approach the alien ship, robot pilots shoot an ultramagnetic ray, rendering the Eagle pilots unconscious. In response, Koenig readies the base lasers to fire at and destroy the ship. Helena and Victor are able to convince him to hold his action though, as the Eagle pilots have not been killed. The robot piloted alien ship swoops in close to Alpha, taking a sensor sweep of their mineral stores and of the Alphan's themselves!

The robot piloted alien ship quickly returns to its mothership, where the robots report to their controllers: a group of disembodied brains from the planet Zamah. The robots relay that there are abundant energy supplies at Alpha that their ship can use, and that the Alphan bodies are perfect transplant vessels for their brains. The brains of Zamah send out new commands to the robots: Attack Alpha! Obtain the minerals and capture the Alphans alive!

Before the alien attack ships can arrive, Victor works out a means of defense against the ultramagnetic weapon and Alpha is able to raise Victor's anti-magnetic shield just in time. The shield holds against the weapons, and security teams out on the lunar surface are able to shoot down all of the alien ships.

Koenig holds a command conference and decides to send an expedition to the mothership, hoping to find out the intentions of the aliens and to prevent a second attack.

Alan, Helena and a group of scientists fly in an Eagle to the alien mothership. Upon entering the ship, they encounter robot guards, which the Alphans quickly dispatch.

Pavel, one of the scientists in the group, tries to convince Alan and Helena that the aliens that built the robots and the mothership must be geniuses and their work should not be destroyed but admired. He believes that their two races must work together, not kill each other. Eventually the Alphans reach the heart of the ship, where they encounter the brains of Zamah. The master brain tells the Alphans that although they have weapons which could kill them, the brains want to live in peace. But the brains of Zamah do need two things from them: the Alphan energy stores, as well as the Alphan bodies for brain transplantations! The master brain tells the Alphans not to worry, that the Alphans won't die, but that they will become enhanced. They will become immortal!