After a cloud of space dust causes a mysterious illness on Alpha, an Eagle crew is send to track the storm cloud. But when the Eagle returns a week later, its only occupant is a huge, terrifying space creature. The cloud returns, and a voice explains to the Alphans that the space creature is their agent, and they want the Moonbase life support system. Tony and Maya fight a desperate battle against the seemingly indestructable creature. At one moment, when both believe their death is imminent, they confirm their love for one another.
A strange cloud appears over Alpha. It begins to interfere with the sensors, and to incapacitate the bulk of the crew, by making them weak and listless.
Eagle 6 is sent to investigate but fails to return after 4 days.
Long after its fuel stores should have been exhausted, Eagle 6 returns to Alpha. Pilot Tom Graham does not respond to Alpha's hails. Sensors detect no life, but the Eagle lands safely. When Tony and the few remaining security guards board, they find a large creature aboard. It attacks and they try to stop it with their stun guns. They fail. Outmatched by the creature, they retreat to Command Center. Tony posts the few remaining security guards to watch the travel tube for signs of the beast.
As Maya tries to get the relative position of the strange cloud, it speaks. Tony asks who they are and it replies that it's beyond their comprehension. It tells them that it has sent for Alpha's life support core. It returns the screens so they can observe the creature leaving the Travel Tube.
Security fires rocket guns at the creature but it shrugs it off and proceeds to beat up the two man team. Tony Sends Maya and Sandra to Medical Center, and has the the computer lock all the doors on Alpha so they will only open and close at his voice command.
He sends Bill Fraser to guard the corridor to Life Support, and tries to lure the creature into a vacuum chamber in Tech Lab 5. Maya wants to help him, but waits, as per his wishes.
Tony gets the creature to chase him into the vacuum chamber, confuses it, gets out, and locks it in. He depressurizes the chamber and lets Alan know what the situation is, as Koenig is still sedated. When he opens the door to make sure it's dead, the creature springs out and attacks. Tony manages to get away and down the hall before it catches up to him.
Alan tells Maya to help Tony. She turns into a mouse and leaves Medical Center via an air vent. She arrives and tries to turn into the creature to even things even things up, but can't. She opts for another and attacks. She distracts the creature long enough to release Tony.
When she can't get away from the creature, Tony releases high pressure carbondioxide which knocks the creature off its feet so they can get away. They go to Medical Center where Helena suggests a heavy duty tranquilizer to use against the creature. Tony uses the commposts to confuse the Creature and keep it from reaching Life Support before they do. They realize they can lead it by taunting it from the screens on the commposts.
Maya has Tony lead it towards the Hydroponics Experimental Section that they can fill with chlorine. Alan calls Tony to find out what the alarm is about, and comes up with a plan to safeguard the Life Support systems. He calls Fraser and has Sandra explain how to build an eletrical barrier across the hallway.
Tony joins Maya in hydroponics. She has it all set up. They only need to get the creature to walk into the trap. Maya turns into an animal from the planet Kreno that is capable of breathing in a chlorine atmosphere. Tony calls to the creature and hides then Maya leads it into the room. The chlorine has no effect so Maya tries the tranquilizer gun. It also has no effect. The creature throws Maya into the door controls shorting them out.
Tony has to break the window to give her an exit. They get away, but Maya is beginning to believe there is no stopping this creature. Tony, unwilling to give up, comes up with an idea to try to attack the cloud to see if they can affect its control over the beast. They go to the weapons section and fire the laser cannon into the cloud. The cloud thins and they see a diamond shape within. They target the object and it splits in two. As they monitor the creature it is disoriented. They think they have succeeded until the two halves rejoin.
The voice from the cloud taunts them. They fire and split it again, then split both halves. All four pieces rejoin to the great amusement of the cloud. Realizing that this, too, was futile, they join Bill Fraser, who has completed his work on the electrical barrier, and wait for the creature to arrive. When it does, it tests the barrier and is repelled. But it gets up and tries again. The barrier weakens with its second attempt.
When they realize that the creature has survived, they know that it will break through shortly. Tony confesses his love for Maya. Their kiss is interrupted when Fraser alerts them to the fact that the barrier won't hold.
Fraser fires the rocket gun in a last ditch effort, but the creature shrugs it off and breaks through the barrier anyway. As it moves into Life Support, Maya realizes that the reason nothing worked against the creature, was that it was, in fact, a robot. It manages to remove the life support core, but Tony and Bill fight the robot, to try to retrieve it. Maya turns into a bee and enters its "ear" to land among the inner workings. She shorts out its ciruitry, finally stopping it.
Meanwhile the cloud has been diminishing in size until it vanishes. Maya visits Tony in Medical Center with an armload of gifts. He asks if she recalls "the wild garbage" he told her when the creature was at Life Support. She promptly takes the gifts and leaves. He laughs knowing she is crazy about him.
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