A spaceship approaching the Moon identifies itself as one of the four "Swift" ships that left Earth in 1996 and disappeared without a trace. Koenig is astonished when he discovers that there are no crew aboard, just a lively computer named Brian the Brain. But when he and Helena go on board the "Swift" ship, Brian kidnaps them.
During a review of the record of Alpha's journey, the computer reports a change in the horizon. Unable to locate the source of whatever is pulling the Moon off course, the Alphans assume the worst... a collision course with a black dwarf. Koenig orders an evacuation of the base.
While doing a visual sweep of the surrounding space, a ship is spotted. Two Eagles are sent to investigate. Bill Fraser contacts the ship. The pilot of the ship identifies it as a Swift, also from Earth, that got lost on a star mission in 1996. The computer verifies his story. The pilot says he has not seen anyone in too long, and asks if he can come down to Alpha for lunch. Koenig agrees.
The Swift lands, and Koenig, Dr. Russell, and two security guards go to investigate the ship. When they board, security takes a look around, but can find no one on board. The voice speaks again and says he will come out to meet them. A robot rolls out from the cockpit to greet them.
He tells them that his crew died while investigating a nearby planet, and that he has been waiting for another mission from Earth since that time. When asked what he should be called, he says the first word he ever spoke was "brain" but he got it wrong and it came out "Brian", and they could call him that. Koenig asks if he has recorded a change in the Moon's course. Brian asks if he means a gravity pull from Planet D, and states that he has not, but would check into it.
After a brief visit to Command Center He says he will return to Swift to investigate Alpha's change of course. He invites Helena along to see if she can offer any information as to why his crew and, more importantly, his Captain died. She accepts, and Koenig asks to go along. After they have left, Maya expresses her concerns about the "brain" to Tony. She asks him to open a channel to Swift, but the computer has ceased functioning and all their communications have gone down.
The Swift has taken off and is flying erractically. John and Helena have been kidnapped by the brain.
Koenig demands that they be returned to Alpha, but Brian threatens to blow them into space if Koenig doesn't put down his weapon. He does, and Brian drops it through a trap door.
Tony goes after the Swift with four Eagles. Brian plans to blind their computers but Koenig asks to speak to them. Brian allows him to, and John orders the Eagles back to Alpha. Tony sends the other Eagles back, but when he discovers the brain's destination, decides to get to Planet D ahead of them.
Back on Swift, Brian is conducting a little experiment. He asks John and Helena if they love each other. They tell him no. To test his theory that they do, Brian has them both step into separate airlocks. He tells them that as he releases the air, they can transfer their remaining air to the other airlock by pressing a black button. As the air gets thinner both John and Helena press their buttons at exactly the same time.
Brian opens the airlocks and lets them out, secure in the belief that as long as he has one, he has control over the other. They land on Planet D and Brian has Koenig put on a spacesuit. John asks why, and Brian tells him that he wants him to walk over to the mothership and bring back it's fuel core. On his way, Koenig finds members of Brians crew lying dead on the planet, without their spacesuits.
He continues on to the mothership. When he boards, he finds Tony and Maya waiting for him. They find the body of Captain Michael, Brian's creator. Maya checks the ships computer and finds that it has been blinded like Alpha's was. That's why the crew went out without their spacesuits.
While trying to find the fuel core, Koenig finds what looks like parts to another brain, and has an idea of how to get at Brian by breaking his mind. Maya says she got a good look at Captain Michael, and turns into a mouse so Koenig can smuggle her aboard Swift in his pocket.
Koenig returns with the fuel core and immediately sets about shaking Brian up. He tells Brian he saw his crew lying dead on the surface, and Captain Michael sitting dead in his command chair. Brian faulters but makes Koenig install the fuel core. Elated at his new sense of freedom, Brian lifts off.
Koenig removes Maya from his pocket and places her on Brian's antenna. Brian wants to know where the mouse came from. Koenig tells him it came from Planet D and that it has a message from Captain Michael. He and Helena accuse Brian of killing his creator because he was working on a better brain. Brian denies it, and Koenig tells him that Captain Michael told him so. Maya tranforms into his "father" and Brian short circuits.
When he is sufficiently disoriented, they push him out of the air lock, but his antenna gets caught, suspending him a short distance from the ship. Koenig tells Tony to dock with the Swift. They have to get the memory core from the brain and get it back to Alpha, but they are not sure if they will be able to as long as Brian's antenna is still working.
Koenig decides to cut it, but Brian threatens to wipe his memory clean if Koenig does. Believing this an empty threat, Koenig decides to go ahead. Brian pleads for his "life" and Koenig makes him a deal. They will let him "live" if he will give them his memory core intact. Brian tells them to take it, that all he wanted was life and friends. He breaks down and starts to cry, much to the surprise of the Alphans.
They return to Alpha with the memory core, get their computer functioning again, and learn that the Moon had never changed course. That was another lie from Brian the brain. After some deliberation, they decide to return Brian's memory core to Swift with their morality programmed in it.
John asks Helena if they have any off duty time that coincides. She tells him it's been used up for the month. He says he had wanted to discuss the "love test". Maya asks about it, and Helena tells her it was a test they failed. John says he thought they had passed it.
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