The Doctor and Romana

The planet Skonnos is dying, and its inhabitants have been promised by an alien bull-headed alien, known as a Nimon, that he can return their empire to greatness. However, this requires sacrifices and radioactive Hymetusite crystals, both of which the Skonnons obtain from the nearby planet Aneth. And so for many years the Anethans have been supplying their young and their minerals to the Nimon on Skonnos – who have now become a part of their legends.

However, the interstellar spacecraft, transporting the latest sacrificial consignment from Aneth, breaks down in space. The ancient spaceship is worn out, and when the Co-Pilot over extends the engines, the Pilot is killed when a control panel explodes. Unbeknown, to the Co-Pilot the TARDIS has materialised nearby and he is about to receive some visitors.

The TARDIS has become immobilised and is in need of repairs and so when The Doctor, Romana and K9 encounter the Skonnan spaceship The Doctor extends the TARDIS door force field to enable them to board the nearby spaceship. While investigating the spaceship Romana is captured by the Co-Pilot, and finds herself imprisoned in the hold along with the Anethans. On the long journey to the planet Skonnos she befriends two of the Anethans Seth and Teka.

The Doctor

On arriving on the planet Skonnos, Romana finds herself, along with the young Anethans, being greeted by the Skonnans’ arrogant leader, Soldeed. He though is being unnerved to see Romana among the group of Anethans. When questioned the Co-Pilot lies stating that she is a pirate who stole aboard and killed the Pilot and so is the reason why they have arrived late.

Soldeed does not believe this and so forces the Co-Pilot into the Nimon’s power complex where he faces certain death. Romana and the Anethans are then loaded up with Hymetusite and are also sent into the Nimon’s labyrinthine power complex.

Arriving on Skonnos

Meanwhile The Doctor and K9 have followed the Skonnan spaceship, in the now semi-repaired TARDIS. But on arriving on the planet and The Doctor finds himself captured and brought before Soldeed – who uses a staff given to him by the Nimon to wield his power over the Anethans and Skonnans. The Doctor soon escapes, and heads into the power complex to escape his pursuers.

Deep in the power complex - whose walls seem to shift and change creating various labyrinthine patterns that all lead to the Nimon - The Doctor and Romana discover that the Nimon are a bull-headed alien race who are in fact a race of intergalactic parasites moving from planet to planet like a plague of locusts. They send a lone representative to an unsuspecting planet, offering help and assistance, and when they have gained the trust of the inhabitants, they arrive in force and drain the planet of all its resources before moving on to another world in the same manner.

The Doctor and Romana also discover that the power complex, fuelled by the Hymetusite, uses a black hole to create a space tunnel through which the Nimons cross from one planet to the next.

Soldeed

Romana travels back along the Nimon’s space-tunnel and arrives in the dying world of Crinoth. There she encounters many Nimon and the last surviving inhabitant, a broken old man named Sezom, who had helped the Nimon establish themselves on his world and now knows they have destroyed it. He has also discovered that when Jacenite is integrated into the staff, that he was supplied with by the Nimon, it has the ability to stun them. He gives Romana a piece of the Jacenite, but is killed by a Nimon while helping her to escape back to Skonnos.

Back on Skonnos, Romana is able to pass the piece of Jacenite to Seth who now has possession of Soldeed’s staff. Seth then uses the staff to stun two of the Nimon. K9 then arrives, having managed to free himself from Soldeed’s laboratory where he had been held, in time to deal with the remaining Nimon.

Soldeed, whose faith has become badly damaged on seeing that there are multiple Nimon and not just the one that he had been led to believe, manages, before he is killed by Seth, to trigger a chain reaction that destroys the power complex, thereby trapping the Nimons on their last home, the dying planet Crinoth.

Later in the TARDIS, as The Doctor sets about completing his repairs on the TARDIS control console, they watch as Seth and Teka pilot a spacecraft away from Skonnos, having been granted their freedom. Elsewhere Crinoth can be seen disintegrating. It seems that the Nimon threat is over for good.