Inferno is the fourth and final serial of the seventh season of the British science fiction television series Doctor Who, which was first broadcast in seven weekly parts on BBC1 from 9 May to 20 June 1970. The serial remains the last time a Doctor Who story was transmitted in seven episodes. This serial was also the last regular appearance of Caroline John in the role of Liz Shaw. In the serial, the alien time traveller the Third Doctor (Jon Pertwee) transports himself "sideways in time" to a parallel world, where a British drilling project causes catastrophic amounts of heat and force to be unleashed when it penetrates the Earth's crust. Plot The Third Doctor and UNIT are called in to investigate a murder at Project Inferno, an effort to drill through the Earth's crust to harness great energies within the planet's core. It transpires that the drilling is producing a green ooze that transforms all who touch it into savage humanoid creatures called Primords, who can only be killed via extreme cold. Unbeknownst to anyone, the project leader, Professor Stahlman has been infected and is in the early stages of the change. After quarrelling with Stahlman, the Doctor attempts an experiment on the detached TARDIS console, but a freak accident transports him into a parallel space-time continuum. In this new universe, where Great Britain is a fascist republic, the Doctor is captured and interrogated by Brigadier Lethbridge-Stewart's counterpart, a sadistic, eyepatch-wearing military commandant known as the Brigade Leader, along with the counterpart of the Doctor's companion Liz, who in this universe became a military officer instead of a scientist. When the drill penetrates the Earth's crust it unleashes immense amounts of heat and poisonous gases, along with more of the ooze, which Stahlman's counterpart uses to transform most of the remaining project staff into more Primords. The Doctor determines that the unleashed energies of the core will eventually disintegrate the planet, and is able to persuade the surviving staff members to help him return to his own dimension and prevent a similar catastrophe. They eventually succeed in restoring power to the TARDIS console despite repeated Primord attacks, but Liz's counterpart is forced to kill the Brigade Leader when he turns on the Doctor, who narrowly escapes as the Project Inferno facility is destroyed by a massive volcanic eruption. Back in his own reality, the Doctor urgently tries to have