When exploring a habitable planet, members of the Alphan survey party vanish without a trace. Are they the victims of an indigenous tribe of Stone Age humanoids? The mystery deepens when a dead caveman is found to have capped teeth. Others soon notice the primitive cave chief and his mate bear an uncanny resemblance to the missing John Koenig and Helena Russell.

Whilst Koenig and Maya are exploring a planet called Luton,which is lush in vegetation, she picks a flower and he helps himself to some fruit. As a result they are put on trial for murder by three talking trees, the Judges of Luton. The trial is by combat and the pair must face three aliens, one with superstrength, one which can render itself invisible and one which can teleport.

Ship's engineer Patrick Osgood believes he can obtain titanium, to make a new heart for his sick wife Michelle, from the catacombs of the moon, using dynamite. The explosion which follows gives him a vision of the future in which the ship is pursued by a fireball and this comes true. Though Helena is making a new heart for Michelle, Osgood becomes impatient and drags his wife back into the catacombs, giving Koenig a double task - to avoid the fireball and save the Osgoods.

The expansive Taybor, an inter-galactic merchant arrives from hyper-space on his ship the 'Emporium'. He is offering to sell things to the Alphans. Koenig realizes that if the Taybor sold them his space-ship, it would enable the Alphans to fly back to Earth, but the price the Taybor is asking for this transaction is Maya.

The Alpha Moonbase needs a rare ore known as Milgonite, which is detected on an extremely dry planet. Koenig leads a small landing force and discovers a glowing rock formation which comes alive and cuts off the party's links with the base. It is a trap - the planet needs water to survive and has lured the travellers there for the water in their bodies.

Koenig and Verdeschi are sucked into a space warp. A feverish Maya is stricken with a fever that causes her to transform into a repulsive space monster.

Some subterranean miners start chanting for a planet that will cause the Moon to pass through a nebula deadly to those living at Moonbase Alpha.

The Alphans encounter an eccentric and intelligent robot who is known as Brian the Brain. Brian's creator Captain Michael and his crew have all died in mysterious circumstances and Brian asks for the help of Koenig and his crew. However, it soon becomes very apparent that Brian is anything but harmless and was in fact responsible for the deaths of Captain Michael and his colleagues. And he is ready to do the same to the Alphans.

The latest extra-terrestials to be rescued by the Moon Alpha Base crew are Pasc and his young son Etrec. They are from the usually peaceful planet of Archaron and they claim that they are victims of a rebellion, engineered by Pasc's wife Lyra. However, Helena discovers that they have both been infected with a virus which makes them considerably less friendly and more deadly than their initial claim.

Several crew members explore the planet Sunin, including botanist Shermeen Williams, who appears to have visionary gifts. She links up with an alien, called Vindrus, who wants her help in transferring his body and that of his race, into solid matter, giving them proper human form so that they can join the universe as real matter. However, for every one of his race made flesh, an Alphan must lose their matter.

A technician falls under an alien influence, accessing classified information before mysteriously dying. Soon after, the Moon is stopped in space by the powerful rays of an alien spacecraft. The aliens' only interest in Alpha is the data held in its computers, information they now plan to obtain through the possessed eyes of their next agent: Helena Russell.

John Koenig finds himself trapped on the planet Zenno, in the home of an alien scientist and his daughter. Advanced two million years beyond Earthmen, the aliens consider Koenig their missing link. Faced with the threat of being treated like an experimental animal for the rest of his life, Koenig uses an unexpected weapon to confound his captor: love.

An Eagle and its crew are crushed to death by an enormous energy field in space. When one of Alpha's astronauts is possessed by the anomaly, he tells them the energy field is a living space brain, which responded to the 'threat' with antibodies Finding the Moon on a collision course with the Brain, the Alphans make plans to avoid the same fate as the Eagle.

The tall and imposing Magus arrives on the base. He claims god-like powers, namely that he effected the Creation. But he is now disillusioned with the way that Life has progressed and wishes to start again. He plans to mate Helena and Tony and Maya with Koenig. But of course he is not God but a renegade cosmic sorcerer, and quite an illogical one at that, who needs to be controlled.

A strange cloud drifts over the base and causes most of the crew to be stricken with illness. A monster, the 'cloud creature' appears out of the cloud and runs amok on the base. A voice from the cloud explains its purpose. The base must give up its life support in order to prevent the cloud from dying. With most of the crew indisposed through illness, it is down to Maya to employ her shape-shifting skills to beat the creature.

A lush Earth-type planet holds the promise of a new home for the people of Moonbase Alpha. When the reconnaissance Eagle returns, it carries an unexpected passenger: Helena's husband, who died five years ago. The mysterious Lee Russell tells the Alphans that death awaits them on the new planet. The Alphans ignore his warning and unknowingly descend into a world of antimatter.

A sinister woman called Zamara materializes on the base, forcing Helena and Tony to accompany her to the planet of Vega, whose natives are anything but friendly. A servant of the Vegans, known only as Number Eight, informs the two Alphans that he and his race are the natural inhabitants of the planet and that Zamara and her race are androids, who, it turns out, want the Alphans to teach them warfare.

Answering a distress signal, Commander Koenig is forced to crash-land his Eagle on Entra - moon of the planet Ellna - which turns out to be the planet's penal colony, and Koenig finds himself a prisoner of the beautiful Elizia and her equally beautiful prison guards.

A pretty, young Alpha technician dies a horrible and unexplained death. Dr. Russell's experiments reveal that one of the crew is possessed of paranormal mental powers and is trying to take control of Moonbase Alpha....

With Maya now a crew member the Alphans discover a young couple called Cantor and Zova who have been in suspended animation for some while. They claim that they are exiles from the planet Golos, following an invasion, and ask for the help of Alphan crew members to restore the planet to them. Helena and Tony accompany them to the planet Golos, where it is apparent that they are not the young innocents they appeared to be.

The Alphans celebrate the arrival of the first child born on the Moon. The blessed event sours when the infant grows into a five-year-old child in minutes. Trying to accept him, the Alphans do not notice that little Jackie Crawford is much more than he seems. When hostile spaceships approach the base, Koenig realises, too late, that the aliens have an agent on Alpha.

Dan Mateo, hoping to unlock the secret of communication with plants, unleashes a killing force from the depths of his own mind. This macabre spectre seeks vengeance for Mateo's horrible death—which has not yet occurred. Bridging the span between science and the supernatural, the Alphans hope to break the cycle and exorcise the ghost without killing the man.

A transmission from Dr. Logan in Texas City leads the Alphans to believe that they can finally land back on Earth, though they have travelled through time and, when they touch down in Texas City, they will be in the twenty-second century. However, due to a hitch, they find themselves in a barren and hostile environment. It is Scotland in the fourteenth century where the Scots are at war with the English invaders.

Whilst he is exploring an asteroid Koenig is taken over by an alien race known as the Kalthon, who replace him with an exact double. In consequence every action ordered by the fake Koenig is solely for the benefit of the Kalthon and to the detriment of the welfare of the Alphans. Helena realizes that something is wrong when 'Koenig' is cold to the touch and needs to convince the other crew members.

The arrival of the Alphans on another planet seems to cause a change in its atmosphere, setting off pollution and poisoning of the water. They meet Zoran, the sole survivor of the last exploratory force, who tells them that the planet is controlled by an immortal being - with whom Koenig must parley if he and his crew are to leave the planet alive.