Commander John Koenig, the new commander of Moonbase Alpha, leads the investigation of a mysterious disease at the station and uncovers evidence of a far greater looming disaster.

A wandering energy force inhabits the body of Alpha technician Anton Zoref, turning him into an energy absorbing being.

After destroying an asteroid on a collision course with the moon, an even larger obstacle appears - an entire planet! On a recon mission, John Koenig encounters an inhabitant who convinces him- on the basis of faith- that the moon and the planet must collide. But no one else supports Koenig's stand.

Moonbase Alpha is attacked and devastated by warships from a nearby planet. With half of its population dead Alpha can no longer survive. Commander Koenig and Dr. Russel go to the alien world to plead for the survivors, but the inhabitants wish no one to disturb their serene existence.

On the ice world of Ultima Thule the Alphans encounter members of lost earth expedition who have achieved immortality- but at a price!

The Alphans encounter the Voyager space probe that has been wandering the cosmos propelled by the Queller drive- a faulty engine system. Following the probe is a fleet of alien ships from a world devastated by the drive.

The Alphans' joy turns to horror when the first child born on the Alpha matures into a five year old in a matter of hours. This is only a prelude to the arrival of formless alien fugitives- who plan to inhabit Alpha's population.

Discredited eagle pilot Tony Cellini is beset by recurring nightmares in which he was the only survivor of disastrous space mission. Now the moon is approaching the same set of circumstances that Cellini encountered.

The Alphans encounter a miles-long ark from the planet Daria, where the inhabitants have a very distinctive class separation.

The moon is approaching a black hole. Professor Bergman is a able to rig up an energy shield around the moonbase, but Commander Koenig feels this is only a desperate measure and has an eagle with six personnel dispatched as the rest of the moonbase await certain death.

Contact is made with the planet Piri, where the main computer created an idyllic life that led to extinction of its population through apathy. Now John Koenig must fight to save Alpha as his people fall under the same fate.

While exploring a cavern in an asteroid, the Alphans release Balor, a sadistic alien who has achieved immortality.

Dr. Russell's presumed-dead husband mysteriously reappears on a reconnaissance mission to a nearby planet.

A vessel of alien pacifists, bound for Earth, lands on the moon. They are greeted as friends by all- except Commissioner Simmons who sees their vessel as way to return home.

While exploring an Earth-type world several Alphans, including Commander Koenig and Dr. Russel, disappear after sighting a strange fog. Shortly afterwards a race of primitive humans are encountered.

A distortion in time produces two separate moons, with two separate Alphas from different eras.

As the Alphans are planning to explore the planet Ariel, a 'missile' attaches itself to the en route Eagle. Upon returning to Alpha, the 'missile' gives the Alphans a lunar atmosphere.

The Alphans encounter Delmer Plebus Powells Gwent, a huge spacecraft which defies aerodynamics and is an extension of Gwent's genius and ego.

Maintenance technician Fred Clifford is possessed by an eerie yellow glow, which ultimately kills him. It transpires that it is coming from a planet called Triton, which captures the Alphans and insists that Helena should become the Eyes of Triton.

After Commander Koening's Eagle crashes on the planet Zenno, his soul is captured and scrutinized by a resident alien, due to the fact that we humans appear to be their missing link.