Turlough and The Doctor

In the far future, on the colony planet Frontios in the Veruna system, some of the last vestiges of humanity are struggling for survival following Earth’s collision with the Sun. Frontios though is being attacked by meteorite showers orchestrated by an unknown enemy responsible for the disappearance of several prominent colonists.

The colony’s leader, Captain Revere, is knocked unconscious when some subsidence occurs in a mine. Security Chief Brazen goes off to fetch help, but when he returns Captain Revere’s body has vanished. Following this incident, Security Chief Brazen orders the research room closed - despite the protestations of the scientist Range and his daughter Norna, who feel that the investigations into the meteorite bombardment that the planet is suffering should continue. Captain Revere’s son, Plantaganet, takes over as leader.

At the same time the TARDIS is hovering above Frontios when it is mysteriously affected by a meteorite storm and dragged down to the planet by gravity. The Doctor and his two companions, Tegan Jovanka and Vislor Turlough, emerge to investigate and they discover the colonists who have been injured by the meteorite bombardment are being helped into the medical area, and the travellers - despite The Doctor’s earlier protestations that he cannot get involved - all help out.

Frontios

The Doctor needs better light in the medical facility. Tegan and Turlough are sent to fetch a portable mu-field activator and five argon discharge globes from the TARDIS but find that the time machine’s inner door is stuck, preventing them from getting beyond the Console Room. Norna, Tegan and Turlough therefore obtain an acid-battery from the research room to power the lights. On their way back, however, they are forced to knock the Warnsman unconscious to avoid capture. Another bombardment occurs and, in the Warnsman’s absence, catches the colony unawares. But when the skies clear they discover that the TARDIS has dissapeared. Plantaganet wants The Doctor killed, but Turlough intercedes, using a surviving hat stand from the TARDIS as a weapon. Plantaganet tries to attack The Doctor with a crowbar but suffers a heart attack. The Time Lord manages to save his life using the battery, but he is later dragged into the ground by the same mysterious force.

Turlough discovers a passage under the research room and he and Norna explore, only for Norna to be captured by the creatures that live there. These are Tractators. Turlough goes into shock at seeing them, as the experience dredges up a deep racial memory of the creatures invading his own planet. The Doctor and Range also find the tunnel, and then so does Tegan.

Tegan and The Doctor

After many narrow escapes from the Tractators, The Doctor and Tegan find their way to the creatures’ control centre and it is there that they meet Gravis, their leader, who explains that the Tractators have been on Frontios for 500 years. They brought the colony ship here 40 years ago, and have been causing the meteorite bombardments for the last 30 years. They need human minds and bodies to run their mining machines, and they plan to replace the current driver - Captain Revere, who is now dead - with Plantaganet. The Gravis also knows of The Doctor and is very interested in his TARDIS.

Meanwhile Brazen, along with his deputy, have been holding an enquiry with Range, Norna and Turlough. Brazen and Range head back into the tunnels, followed by Turlough. In their absence, the research room is attacked by an orderly named Cockerill and a group of retrograde colonists who feel that the present order is breaking down and want their independence.

When Turlough catches up with Brazen and Range, Range goes back to check on Norna’s safety. Turlough rescues Tegan, who has been held in a gravity field by a Tractator, and they then move on to rescue The Doctor. The Doctor tampers with the mining machine and causes the Gravis to suffer an electric shock. The creature falls unconscious and all the other Tractators then mill around in confusion. Plantaganet is rescued from the machine but, in a struggle, Brazen falls into the driver’s seat and becomes hooked up instead. This though causes the machine to go out of control and it crashes into a wall.

Brazen

The Doctor then discovers that the Tractators are building a gravity motor with which to pilot the planet out of orbit. Plantaganet reveals that there are in fact two mining machines, and Turlough remembers an important fact about the creatures: if the Gravis is removed from the others, they all cease to be intelligent and return to a docile state.

Wandering in the tunnels, Tegan is horrified when she comes across bits of the TARDIS’s inner walls. While being chased by some Tractators led by the Gravis, who has now regained consciousness, she comes upon one of the TARDIS’s inner doors. Going through it, she finds herself in the TARDIS Console Room, which has bits of rock wall mixed in with its normal walls. The Doctor, Turlough and Plantaganet are already there. The Doctor ushers the Gravis in and then goads it into reassembling the TARDIS using its power over gravity. When the outer plasmic shell forms, the Gravis is effectively cut off from its fellow Tractators, which revert to a harmless state.

The Doctor then drops the Gravis off on the uninhabited planet of Kolkokron. Returning to Frontios, The Doctor gives Plantaganet the hat stand as a farewell token and asks that his own involvement in the affair not be mentioned to anyone – especially the Time Lords.

Once the TARDIS has dematerialised from Frontios, its engines start making a worrying noise when an outside influence starts to affect it. Unable to do anything The Doctor tells Tegan and Turlough that something is pulling them toward the centre of the universe. He does not know what it is, but anticipates that they are soon going to find out…