Koenig is finishing a staff meeting and Commissioner Simmonds speaks up, complaining that they're more focused on adapting to their existing circumstances then finding a way to return to Earth. Koenig points out that it's impossible and Dr. Russell doesn't want to encourage false hope. Simmonds insists they should focus on going home to boost morale, but Koenig refuses to entertain his suggestions. Sandra calls in to report they've detected a manned spacecraft approaching the Moon. Koenig orders Alan to intercept the object and two Eagles depart.
As the Eagles approach, Alan reports that the ship is out of control and falling toward the Moon's surface. They follow it down but can only watch as it makes a rough landing. Koenig, Bergman, and Russell take a rescue Eagle out with a security team. Simmonds suggests he should come along and Koenig tells him he doesn't need a politician.
The rescue Eagle approaches the crash site while Bergman speculates that the spaceship crew deliberately picked them out. Carter docks with the alien spacecraft and leaves the rescue pod behind while returning to Moonbase Alpha. Koenig and his team are unable to confirm any life signs inside. They gain entrance and find the ship's crew in suspended animation within transparent cases.
As Moonbase Alpha provides gravity and atmosphere for the ship, Simmonds complains about the lack of a visual link. They finally establish visual contact and the Alpha crew watch as Dr. Russell is forced to admit that the alien crew appears to be dead. Bergman confirms they've taken every possible precaution and the next step is to break the seal on one of the cases. Sparks fly as the first casing is filled with atmosphere. The alien inside is reduced to dust. The control circuitry starts up and the five remaining aliens begin to revive. Their leader examines the remains of his dead comrade while Dr. Russell apologizes. He takes Russell's hand and leads her over to the case, and then he and the others perform a brief ritual.
On Alpha, Simmonds paces irritably waiting for a response. Koenig calls to tell them that the aliens will be flying their spaceship in on half power. Simmonds is the first to get there and demands that Koenig introduce him. Koenig introduces the alien captain, Zantor, who asks what Simmonds' status is. Simmonds says he represents Earth's authority and that the individuals who killed their comrade will receive justice. Zantor acknowledges that the death was an accident and he won't seek judicial revenge. As Zantor and his people are taken to their temporary quarters, Simmonds warns that Zantor may not be as friendly as they seem.
Later, Zantor offers Koenig and the others gift eggs from their home planet of Kaldor, that was dying three and a half centuries ago. The Kaldorians sent out craft to any planets they thought could support life. Zantor's ship was programmed to land on the Moon and then they would proceed to Earth, but they're aware that the Moon is no longer in Earth orbit. Simmonds wonders if their computer can calculate the current location of Earth. Zantor says that they will proceed to Earth but would destroy themselves if they weren't accepted. Dr. Russell offers to run tests to make sure the Kaldorians are compatible with Earth's atmosphere. As they leave, Simmonds suggests to Koenig that they seize the Kaldorian spaceship, and that Zantor and his people are expendable.
As Dr. Russell runs her tests, Zantor explains that they use a superior form of suspended animation that holds all cell activity in stasis, and can be adapted for human use. She confirms that Kaldorian life is compatible with Earth, and he notes that it will take 75 years for them to reach Earth. They return to the Kaldorian ship and Zantor notes they will be ready to leave within 20 hours. He observes that there is a vacant space and they can take one Earthling with them. Koenig tells Dr. Russell to check the process. Simmonds goes with Koenig and insists they take the ship and send six people back. Koenig points out that in 2074, life on Earth may be unrecognizable but Simmonds thinks it's worth the risk. Koenig refuses, saying that the computer will choose one person at random but he'll exempt himself. He has Kano start programming the computer to make the decision.
Later, Bergman contacts Koenig to tell him they have an emergency on the Kaldorian craft. He arrives to learn that they experimented on Dr. Russell and they're unable to revive her. Dr. Mathias and Zantor work together to revive her without success. While they wait, Alan computes the location of Earth and Controller Morrow reports the ship will be ready on schedule. Mathias asks him to return to the spaceship where Zantor notes that the computer's profile wasn't sufficient to understand the human spirit. The Kaldorian computer does but Zantor warns there is a possibility of damage to the brain. Zantor proceeds and manages to revive her.
The computer announces its choice and picks three staff members. However, Koenig refuses to read the list until Russell has declared the process safe. Koenig warns that they're not sure if the Earth is even there, and that regardless their families won't exist. In Koenig's office, Simmonds insists that Koenig should have made the decision and chosen him. As Zantor, Bergman, and Russell arrive, Simmonds switches his comlink for Koenig's comlink unit. Simmonds slips away while Zantor explains that they will have to make a matrix of the specific person chosen.
Simmonds takes a pod to the power station and stunts the guards. In his office, Koenig wonders what Bergman and Dr. Russell will do if they're chosen. Koenig notices that his comlink has been switched and orders an alert. Simmonds makes his way into the power station and tells the technician to do what he tells them. Koenig contacts him but Simmonds ignores him and has the technician open up the main control panel. He removes the main power unit and tells Koenig that if he isn't allowed on board the Kaldorian ship, he'll destroy the converter unit. With no other choice, Koenig calls Zantor back to the command center. Carter suggests they try to trick Simmonds but Bergman warns that if the converter is destroyed, they're all doomed. Zantor arrives and Koenig explains the situation. He advises him to accept his terms and the crew agrees they'd be better off without him. Zantor offers himself as a hostage to guarantee Koenig's behavior.
Simmonds collects Zantor, and the Kaldorian captain wishes them well while admitting it's a shame that Simmonds will succeed through the use of force. Aboard the Kaldorian spaceship, Simmonds insists that the aliens enter their hibernation pods first. Once they're safely secured, Simmonds enters the sixth pod and they all enter suspended animation as the ship lifts off.
A few hours later, the ship travels through the vastness of space and Simmonds wakes up. Sealed within the pod, he uses the comlink and tries to hail Earth. They receive his transmission on Moonbase Alpha. They realize that Zantor didn't have time to adjust the matrix to Simmonds' bio pattern. Simmonds activates the clock on the comlink and realizes that he's only been gone a few hours… and he has a 75-year trip ahead of him with only enough air, food, and water for a few hours. He begs Koenig for help but there's nothing they can do.
As the Alphans go back to their duties, Dr. Russell wonders who the computer finally picked. Koenig reveals that it chose Simmonds.