Doctor Who: Earthshock (1982) written by Eric Saward and directed by Peter Grimwade
The Fifth Doctor (Peter Davison) lands the TARDIS on Earth in AD 2526. Actually, he lands inside the Earth, in some caves where, naturally, trouble is brewing. An expedition of geologists and paleontologists were wiped out by a mysterious force. One survived and she is leading a military group back into the caves to find out what happened. After a typical misunderstanding (surely the Doctor and his companions must be guilty since they are in the caves!), the Doctor unites with the 26th century earthlings to fight the menace--the Cybermen. The Cybermen want to destroy the Earth, and when their first plan is foiled, they have a more subtle plan that will cost the Doctor dearly.
The Cybermen are an interesting opponent in this story. They have a history of losing to the Doctor, so once they recognize him, they look for vengeance as well as for the destruction of the Earth. The hyper-logical Cybermen taunt the Doctor for being emotional and therefore weak. The Doctor gives as good as he gets. The Cyberman costume is a little weird because their face's chin plate is transparent. Viewers see a grey chin as the Cybermen talk. While it's a reminder that they aren't just robots, it doesn't help them to be scary. Also, the leader is a bit shouty and does say "excellent" several times as if he were Mr. Burns from The Simpsons.
Peter Davison's Doctor has a fairly interesting relationship to his three companions in this episode. Tegan (Janet Fielding) and Nyssa (Sarah Sutton) provide some technical support and some humanizing moments for the Doctor. Young Adric (Matthew Waterhouse) is a mathematical prodigy from another planet who wants to go home. The Doctor at first refuses, though Adric plots a course anyway. Their interactions are interesting and come to a poignant ending.