Technician Ted Clifford is working at a viewport in the control centre when a glowing red sphere appears on the horizon. A beam of energy surrounds Clifford's head. Entranced, he walks over to the computer and starts transmitting information, manipulating the controls at superhuman speed. When first Kano and then Paul try to stop him, Clifford grabs them with superhuman strength and casually tosses them aside. Koenig and Dr. Russell are summoned but are equally helpless. Clifford finally snaps out of his trance and begs them for help, and then collapses to the floor, dead.
The sphere emits a beam of energy, surrounding the moon in a ring of light. The moon jerks to a halt and everyone is thrown to the floor. They realize that they're locked in the object's orbit as the inhabitants of the sphere contact them, informing them they are captives of the planet Triton.
Power feeds drop to minimum and several of the eagles are damage. As they struggle to establish communications, Dr. Russell performs an autopsy on Clifford and Professor is unable to find the planet Triton in the astronomy records. They are unaware that the Tritonians are watching them via remote, focusing particularly on Koenig and Dr. Russell
Koenig goes to the infirmary where Dr. Russell explains that Clifford died of massive cerebral melt down. A small sphere of energy appeared within his brain in the sections where the visual and data processing centres are located. She and Mathias conclude that the energy sphere somehow turned Clifford into a living computer. Koenig has Carter and Donovan approach the sphere in an Eagle. It surrounds them in a beam of light and forces the ship away. Carter seemingly manages to land the Eagle on the lunar surface, although Donovan is killed in the crash. Koenig and Dr. Russell are forced to take a rescue team out on foot. As they proceed, the command centre warns that the Tritonians are jamming their sensors and possibly preparing to launch an attack. Koenig heads for the Eagle to seek cover but the Triton sphere traps Dr. Russell in an energy beam. When Koenig goes to her aid, the energy beam knocks him back and teleports her away.
Dr. Russell finds herself in a black void within the Triton. The same voice that contacted Moonbase Alpha speaks, telling her not to be afraid. It identifies itself as the Eyes of Triton and tells her that she will act as its servant.
Koenig wakes up in the infirmary and Bergman brings him up-to-date on Dr. Russell's situation. The commander has Bergman work to increase the anti-grav shields on the Eagles so they can penetrate the Triton sphere's force field. Carter wakes up and admits that he had nothing to do with landing the Eagle. Since the Tritonians clearly have enough power to defeat any measures they can take, Koenig wonders why they are taking a roundabout way to achieve their goal: the abduction of Dr. Russell.
A short time later, Bergman confirms that he's enhanced the anti-grav shielding. Koenig prepares to leave with a co-pilot, only to discover that Carter insists on going with him. They go toward the Triton sphere and their booster anti-grav shields let them penetrate its force field. The Triton sphere drops all defenses and the Eagle rockets in at several Gs. Unable to move due to the pressure, Koenig and Carter just manage to switch the ship's controls to automatic before they pass out. The Alpha command crew brings them back by remote.
A glowing red energy ball hovers over the base and when the crew emerges to investigate, they find Dr. Russell standing on the moon's surface. Dr. Mathias examines her and discovers that she's seemingly blind. However, Dr. Russell can see although her vision is only in two dimensions, as if someone or something was intercepting some of the visual signals her brain receives.
The Triton sphere flares up and Dr. Russell goes into a trance as energy surrounds her head. Koenig tries to approach her but realizes that the light forms a lethal force field. Koenig warns everyone to stay away from her as she teleports out of the infirmary and goes to the control centre. Once there, Dr. Russell activates the computer and begins transmitting more classified information. Bergman confirms that she is particularly interested in the life support systems. After a few minutes she collapses and reverts back to normal.
Bergman concludes that the beings within the Triton sphere are bodiless intelligences, giving them the advantage if they can penetrate the force field. Dr. Mathias determines that a similar energy sphere has appeared within Dr. Russell's brain, in the same location as the one in Clifford's brain. Because the Tritonians placed it directly in when they had her aboard their ship, she is weathering the process better but the process will eventually kill her.
Going over the readings, Bergman concludes that the sphere is actually an uninhabited reconnaissance probe and the "Tritonians" within are artificial intelligences. The planet Triton was blown up two million years ago and the probe is now obsolete. Koenig comes up with a plan to have Kano jam the computer link between Dr. Russell and the Triton sphere. That will cause the force field to drop long enough for Koenig to get onto the sphere and convince the controlling intelligence that its function is no longer necessary.
Koenig, Carter, and a security team depart for the Triton sphere in Eagle One the next time that the probe activates Dr. Russell. As she begins using the computer to transmit more information through her own brain, Eagle One approaches the Triton sphere. Kano jams the computer and the force field drops. Koenig lands the ship and goes out with a security team while Carter remains at the control.
Inside, the security team is teleported away. Proceeding inward, Koenig finds the central intelligence: a large glowing eye like organic computer. It apologizes for the death of his people and says that it has been watching earth for centuries. When Koenig challenges it, it explains that the people of Triton believed that Earth was a threat and sent it to gather information for a retaliatory strike. Koenig explains that its home planet no longer exists and has Bergman and Kano feed it new information from the Alpha computer, confirming that its point of origin has been destroyed. The Triton intelligence, convinced, begins to self-destruct. Koenig finds the security team and they return to Eagle One, lifting off just in time to get clear of the sphere before it destroys itself.
Later, Mathias confirms that the energy sphere within Dr. Russell's brain has disappeared and she' back to normal. Bergman wonders if despite all the vast knowledge that the Triton sphere contained, that may not have been the answer after all.