In the Jungle

After dealing with the Zygons (see the previous story "Terror of the Zygons") The Doctor, and his travelling companion Sarah Jane Smith, use the TARDIS to travel back to London. However, on their way the TARDIS picks up a faint distress call, which The Doctor detects is coming from the edge of the known universe, and he promptly resets the co-ordinates so they can assist whoever needs rescuing.

The TARDIS soon arrives on the planet Zeta Minor in the Morestran year 37,166, where The Doctor and Sarah discover that a Morestran scientific expedition has fallen prey to an unseen killer which is slowly killing everyone. Now only Professor Sorenson is left, and he is not all that he seems to be.

The TARDIS's arrival coincides with that of a military spaceship from Morestra, sent to investigate exactly what has happened to their expedition. The Morestrans discovers, when they question Sorenson, that he is confused and unable to supply the answer as to what has killed the members of the scientific expedition. Then when members of the military crew start dying, the logical suspects become The Doctor and Sarah, strangers who just happened to have arrived as the killings started.

Sarah by the TARDIS Console

The culprit is eventually revealed to be a creature comprised of anti-matter that has come from a universe of anti-matter. When seen it is a shimmering red outline of a huge creature. It is retaliating for the removal, by Sorenson, of some anti-matter samples from a crossing-point of the two universes, a bottomless black pool located deep in the jungle.

When The Doctor discovers the black pool leading to the universe of anti-matter Sarah, who is watching events from the bridge of the Morestran ship, is alarmed when the anti-matter creature emerges from the pool and The Doctor is dragged forward and then topples over the edge. Thankfully he eventually appears from the pool – seemingly unharmed.

What is it?

The Morestrans then have a shock when they try to take off in their spaceship. They soon discover that regardless of how much power they use that they are slowly being dragged back towards the planet. The creature, The Doctor deduces, will not allow the Morestrans to leave with the anti-matter on board their spaceship and despite how hard they try, the forces that hold the spaceship intensify until they are held stationary in space, struggling against the increasing pull back towards the Zeta Minor.

The Doctor realises that Sorenson himself has become infected with anti-matter and is gradually transforming into an anti-man, a bestial creature capable of draining the life from other beings.

The Morestran commander, Salamar, who has become increasingly unstable under the pressures of command, finally cracks, and goes after Sorenson with a neutron accelerator. Instead of killing him, the radiation from this causes the creature, which Sorenson has become, to multiply. The spaceship is soon overrun with snarling deadly creatures, able to walk through doors and intent on sucking the life from the crew.

The Doctor and Sarah

The Doctor manages to find the original Sorenson anti-man and takes him back to the planet, in the TARDIS, and throws both him and his samples into the pit, fulfilling a bargain he earlier made with the anti-matter creature when he earlier he had fallen into the black pool.

Sorenson then reappears unharmed and The Doctor returns him to the Morestran spaceship. Now freed of the planet's influence it starts its long journey back towards Morestra.

The Doctor and Sarah then leave, in the TARDIS, so as to keep their original appointment with The Brigadier in London.