In the main control room, technician Ted Clifford is working at one of the portals when a glowing red object appears on the horizon. Clifford sees the light and is taken over, and then walks to the control panel and starts adjusting the computer at lighting speed, transmitting classified information. When Kano tries to stop him, Clifford grabs him with superhuman strength and tosses him casually away. Paul attacks him but is equally helpless. Sandra calls Koenig and Russell to the control room but they're equally unable to stop him. Clifford finally snaps out of it and begs them for help before collapsing, dead.
A beam of light suddenly shoots out from the object, encircling the moon in an energy field. The shock throws everyone to the floor. The crew checks out all systems and they briefly get a picture of the object before the systems shut down. Sandra confirms that the object is getting closer and Koenig realizes they're locked in orbit. They receive a transmission informing them that they are prisoners of the planet Triton.
The crew determines that power is at minimum and transport systems are cut off, with four Eagles damaged. The computer is unable to provide any useful calculations and Koenig tells Paul to establish communications. He then orders Dr. Russell to perform an autopsy on Clifford to learn what they're up against and turns to Bergman for answers. The professor hasn't heard of the planet Triton but warns that the natives are undoubtedly watching them.
Triton secretly watches the base through the internal monitors, focusing particularly on Koenig.
Dr. Russell and Mathias inform Koenig that a sphere of energy burned out most of Clifford's brain after expanding the sensory sections of his brain. As they discuss the matter, they're unaware that Triton is now focusing on Dr. Russell. Meanwhile, Koenig tells Carter to prepare for a possible landing but Carter disagrees, noting they've already killed Clifford. Koenig overrides him and Carter and a co-pilot, Donovan, depart in an Eagle. They approach Triton and a beam of light surrounds the ship. Carter is unable to break free and the Eagle is repelled violently back toward the moon. Donovan is killed and Carter is unconscious. The Eagle crashes on the surface. Koenig and Russell lead a rescue party on foot to rescue them while the crew realizes that Triton has jammed their scanners and may be preparing an attack. Koenig decides to continue on and Triton fires an energy beam, hitting Dr. Russell. When Koenig goes to her aid, a blast of energy knocks him unconscious.
Dr. Russell finds herself in a black void wearing golden robes. The voice of Triton tells her not to be afraid.
Koenig wakes up in the infirmary and Bergman tells him that Triton has taken Dr. Russell. Koenig has Bergman increase the strength of the anti-gravity fields on an Eagle so they can penetrate Triton's shields. Bergman suspects that Triton specifically targeted Russell but Koenig points out that their opponents have enough power to take what they want without tricks.
Dr. Russell tries to converse with Triton, and is informed that it is in fact the Eyes of Triton. It records everything that exists, and Dr. Russell will act as their servant.
When Carter revives, Koenig interrogates him but is unable to learn anything useful. He's surprised to hear that the Eagle landed despite the fact he was unconscious.
Bergman notifies the commander that he's created an anti-grav shield that will allow them to land. A pensive Koenig wonders will happen once they hit the barrier. Koenig prepares to depart and discovers that Carter has taken the place of the designated co-pilot. They lift off and approach Triton. Koenig switches the anti-grav shield to full power despite Bergman's warnings and they start to get through. Triton reverses the force field, pulling them in, and Koenig manages to cut the engines before he ad Carter pass out from the gravitational strain. The Eagle goes back to the moon on automatic and the staff land the ship by remote.
A glowing red sphere approaches the moon and hovers over the base. They open the airlock doors to find Dr. Helena Russell. Dr. Mathias examines her and determines that her biosigns are normal. As she gets up she feels a brief surge of dizziness. She tests her vision and discovers she lacks visual overlap, and Dr. Mathias admits that the tests show that she's blind. As they consult with Bergman, Dr. Russell remembers that she talked to Triton and told them they were willing to help. Bergman warns that the Tritonians have the power to transmit matter and use an oxygen atmosphere.
Triton flares up and Dr. Russell goes into a trance as her head glows red with energy. She turns and then teleports through a door, heading for the computer. Koenig goes after her and tells Bergman to warn everyone not to interfere with her. She goes to the command center and begins activating the computer, just as Chandler did. The information she's sending is a breakdown of their life support systems. Bergman realizes that the information is being transmitted through Dr. Russell. She comes out of her trance and then collapses against the panel.
Bergman speculates that the Tritonians are intelligence without a body and Koenig believes that they have the advantage since they can still move. Dr. Mathias confirms that the same energy sphere is inside of Dr. Russell's brain that was in Chandler's, and she survived the process because they implanted it directly. Dr. Russell functions as a human conductor, but even with the direct implant her brain can't take much more.
The professor believes that the main sphere is a reconnaissance probe sent from the planet Triton. Bergman has checked the star charts and determined that Triton blew up. Koenig suggests trying to convince the probe that its mission is obsolete so that it will surrender its hold on them. The commander proposes that Kano jam the link between Triton, Dr. Russell, and the computer. That will drop the force field and give him 13 minutes to land and convince them their home planet doesn't exist. Koenig explains the plan to Dr. Russell and she realizes she has no choice but to participate.
Koenig, Carter, and a security team depart as soon as the Triton probe activates Dr. Russell again. She goes to the control room and begins activating the computer. Koenig lifts off and heads for Triton. Kano jams the computer, Dr. Russell collapses, and the force field drops. The Eagle lands safely while Kano feeds in the information so that Triton only receives the data they want it to receive. Koenig has Carter stay at the ship while he takes the security team out into a vast dark chamber.
Triton reestablishes its control on Dr. Russell and she returns to the computer.
The security team is teleported away and Koenig finds himself viewing an image of Dr. Russell tapping into the Alpha computer. The image disappears and Triton greets Koenig. It apologizes for the death of his people and shows itself as a glowing giant eye creature. Triton says that it has been watching Earth for centuries and finds it primitive. They plan to use Koenig to replace Dr. Russell when she dies from the strain, and believe Earth is preparing to invade Triton. Koenig has Bergman feed the information through showing that Triton no longer exists. The Triton sphere begins to destroy itself and Koenig is reunited with the security team. They get back to the Eagle and lift off just in time as the Triton sphere blows up behind it.
Later, Mathias confirms that Dr. Russell is fine and Bergman is left to wonder if knowledge isn't the answer after all.