Inferno (Doctor Who) - Plot

Plot

"The Inferno" is the nickname given to a project to penetrate the Earth's crust to reach pockets of Stahlman's Gas, which is theorised to be able to provide boundless amounts of cheap energy. Professor Stahlman himself is ill-tempered and obsessive about any interference with the progress of his work. Sir Keith Gold, the project director, is concerned about this and tells Petra Williams, Stahlman's assistant, that he is calling Greg Sutton, an oil drilling expert, to consult on safety issues. UNIT is overseeing security at the project. The Third Doctor is also present, as he is using the output of the project's nuclear reactor to power experiments on the TARDIS console, which has been removed from the TARDIS, hoping to repair it in order to end the exile on Earth imposed on him by the Time Lords (The War Games).

The project, however, has its own problems. Harry Slocum, a worker repairing one of the drill pipes, encounters a toxic green slime seeping out of the pipe that rapidly mutates him into a subhuman primordial creature, who kills several technicians and a soldier. A quantity of the substance siphoned into a jar also mildly scorches Stahlman's hand. Meanwhile, whilst operating the TARDIS console, the Doctor vanishes into thin air before a shocked Brigadier and Liz and arrives in a parallel universe. On this Earth, Great Britain is a Republic under a Fascist regime; it is implied that the British Royal Family was executed in 1943. The Inferno project is also ongoing, though having progressed farther in this reality. The project is run along the lines of a scientific labour camp, under the auspices of "Director Stahlmann," this reality's counterpart to Professor Stahlman. The Doctor, captured and under interrogation by the British Republican Security Forces, encounters brutal, alternate versions of his friends - "Brigade Leader" Lethbridge-Stewart, "Section Leader" Elizabeth Shaw, and "Platoon Under Leader" Benton. Sir Keith Gold did exist in this universe, but has been killed in a car accident arranged by Stahlmann. The Doctor tries to convince the parallel versions of his friends that he is from another universe, but they believe he is trying to feign insanity. The Doctor manages to escape his cell and tries to stop the drilling but is discovered. The Doctor pleads for them to stop, telling them that the screeching noise coming from the drill shaft is the sound of the planet "screaming out its rage."

As Stahlmann holds the Doctor at gunpoint with the Brigade Leader's pistol, an earth tremor rocks the installation and most of the technicians and RSF troops flee the complex in terror. The temperature rises rapidly as more green slime oozes out of the drill shaft. Stahlmann and most of the scientists become primords. The Doctor believes that the parallel Earth is doomed and tries to convince the others that he can stop this from happening in his own universe if they will help him to return, but refuses the Brigade Leader's demands to save them too. Finally agreeing to help the Doctor, the group fights off the hordes of primords, including an infected and mutated Benton, with fire extinguishers, as the creatures thrive on heat and are vulnerable to cold temperatures. The parallel Petra, with Sutton's help, manages to feed power to the TARDIS console. At the last moment, the Brigade Leader snaps and threatens to shoot the Doctor if he doesn't save them, but is shot dead by Section Leader Shaw. The Doctor manages to return to his own universe just as a wall of lava sweeps towards the hut.

The Doctor returns to his own reality. After waking from a coma, the Doctor learns that since Sir Keith Gold has survived his car accident in this universe, it means that "the pattern can be changed" and this Earth need not perish as the parallel one has. The Doctor goes to the main control room and tries to stop the project by smashing the equipment, but he is restrained by UNIT troops. The drilling has almost reached the critical point, "Penetration Zero," but Sir Keith is reluctant to shut down the project without sufficient proof. However, this world's Stahlman has also ultimately mutated into a primord, and attacks the control room before being killed by the Doctor and Sutton with fire extinguishers. Petra has the drilling stopped, and with the project abandoned, Sir Keith announces his plans to have the shaft filled in. Shortly before the nuclear reactor is deactivated, and after an altercation with the Brigadier, the Doctor tries to repair the TARDIS console one last time, but lands himself several hundred yards away at a nearby rubbish dump.