Project Inferno is designed to drill down to the center of the Earth, where it will release a wonderful new energy source called Stahlman's Gas named after the project's director. But the Doctor realizes that unleashing Stahlman's Gas will have horrible consequences from the planet, fears confirmed when a power surge in the TARDIS console sends him to a hostile parallel universe where the project is nearing completion.
Did You Know?
Originally SGT Benton role was to be a nameless SGT, however Directer Douglass Camfield decided to make the role Benton to allow his Protege John Levene to expand his acting career, this combined with Previous producer Derick Sherwin's suggestion that the 1970 series feature Benton, both of these factors led to Levene receiving a regular contract for the following year. See more
International broadcasts and the VHS release of this serial include an extra scene in episode 5 that was not broadcast in Britain. For the 2006 DVD release, this scene has been removed and included as an extra feature. The scene featured the voice of Jon Pertwee as a radio announcer. See more