On its long travels through the universe, Moonbase Alpha approaches an unknown planet. Hope for a new homeworld awakens once again in the hearts of the crew...

Initial sensor indications show Alpha is approaching an inhabitable, terrestrial type planet. Calculations show the Moon will be within Eagle reach of the planet for just a 56 hour period, providing only a short window for a reconnaissance Eagle to reach the planet and to determine if Alpha should perform Operation Exodus.

A laboratory equipped Eagle is launched for the planet, with John, Helena, Victor, Alan and a team of scientists onboard. Upon arrival, the lab is set up and Alan and John set off on a recon flight in search of civilization. John and Alan quickly come upon the ruins of an ancient city and land the Eagle to investigate. Upon landing, John and Alan immediately hear a loud hissing sound and soon the Eagle is surrounded by giant ants! The ants grab a hold of the Eagle and their strength prevents Alan from lifting off. Soon the Eagle is dragged across the surface of the planet back to the ant nest.

Victor is unable to raise Koenig by commlock and realizes the mission is in trouble. Victor is able to locate the Eagle 150 kilometers from the lab, and sets out in a moon buggy with three others to investigate. After arriving at the ant nest though, they are spotted by one of the giant ants. They are barely able to stun the giant insect and flee from the swarm of ants alerted to their presence. Victor realizes that in order to rescue John and Alan a means of killing the ants is required.

When Victor returns to the lab he meets a group of inhabitants of the planet Onatu that have come to invite the Alphans to their city and to meet their queen. While the scientists now begin to work on a method to kill the giant ants, Victor and Helena are taken to a fairy-tale style city in the center of a nearby lake - which is the only safe place from the ants.

In the alien city they meet Queen Hara, who relates the tale of how early Onatu scientists used genetic mutation to alter ants so that they could be enlarged and used as beasts of burden in agriculture. The mutation method instead created monster ants, and before they could be killed the ants escaped, multiplying into the millions and destroying their people and civilization. Victor then relates the story of the Alphan odyssey and asks for asylum. Queen Hara tells Victor that if they are able to find a means of killing the ants, then the Alphans are more than welcome to come live on the planet.

With only 35 hours remaining to make a decision on Operation Exodus, the scientists are still working to create an insecticide that will kill the ants - when Victor and all the scientists suddenly become dizzy. Helena prescribes a circulation enhancing medicine, which is only able to temporarily improve everyone's health. Victor eventually determines that there is a natural element in the air of Onutu that is slowly killing the Alphans. It is now a race against time to create an insecticide and rescue John and Alan before they all succumb to the deadly poison.