Inferno is the name of a top-secret drilling project to penetrate the Earth's crust and release a major new energy source. A crisis develops when a noxious liquid leaks out as drilling progresses—the green poison has a grotesquely debilitating effect on human beings. As the Earth's plight worsens, the Doctor is trapped in a parallel world, unable to rescue the planet and its inhabitants from the destructive force of Inferno...