In the conclusion of the six-part story "Invasion of the Dinosaurs," eco-fanatics Grover (Noel Johnson) and Whitaker (Peter Miles) step up their efforts to hurl the world back to the Prehistoric Era. The Doctor (Jon Pertwee) and his UNIT colleagues manage to raid the villains' underground headquarters, but Grover has already activated the device that will enable him to carry out his crack-brained scheme. Written by Malcolm Hulke, "Invasion of the Dinosaurs, Episode 6" was first telecast on February 16, 1974. ~ Hal Erickson, Rovi