Doctor Who-Earthshock

                          On Earth in the year 2526,a mining expedition led by Professor Kyle and a Lieutenant Scott are using advance thermal equipment to search for missing members of their team. On board the TARDIS meanwhile Adric declares to the doctor that he is unappreciated by the doctor,Tegan and Nyssa alike. And that he had calculated a way back to E-Space where he wishes to return. The ensuing argument leads the doctor to take the TARDIS to the underground caverns of the mining expedition. When walking within the caverns the doctor,Tegan and Nyssa find a massive amount of dinosaur remains within it-as well as natural sulphurated lighting.  Of course the presence of the two hearted time lord with his companions into their mining setup lead Scott and Kyle to believe they are responsible for the missing miners.
   
                        Before the doctor can debate the innocence of him and his companions with the expedition,a trio of Faceless androids launch an all out attack on the miners-unknowingly being used by a Cybermen vessel to specifically track down the doctor. While hiding from the androids,the doctor locates a metal door which the androids seem to be deliberately avoiding. While Scott and his offers continue their fire at the androids,the doctor manages to breach the door and inside finds a bomb that is set for a swift detonation-one powerful enough to destroy the Earth from the inside out. The doctor manages,with the help of Adric's calculations to disarm the device. Upon return to the TARDIS with a now grateful Scot and Kyle and mending the fence with Adric,the doctor informs all of them that the bomb in the caverns was sending a signal to Sector 16 and he intended to investigate the situation further-after which Kyle and Scott insist on joining in gratitude.

                   In that sector,a freighter on route to Earth to make its delivery detects an unexpected disruption in the neighboring sector that indicates a possible delay in their delivery. When the doctor's TARDIS appears, the   freighter's security chief Ringway finds two crew members murdered with the doctor and Adric investigating. While planning to execute them, freighter captain Briggs insist they be bought to the bridge-where he disbelieves the doctor that he and Adric had not killed her two crew members. Impatient for the doctor and Adric's delay,Scott leads Tegan and some of his officers in entering the freighter on the offensive. As the doctor is fending off a near mutiny between the crew and Briggs over her seeming inability to trust the doctor,the freighters internal sensors indicate the true source of the murders and the disruption: the same Cybermen Tegan and Scott have encountered. Using a flux of the ships antimatter power source to trap one of the Cybermen in the entrance to the bridge,the Cybermen reveal their plan to the doctor.

                 The Cybermen plan to re-inhabit the Earth after accelerating the freighters at warp drive so the freighter will become a bomb that will crash into the Earth-destroying a multi national Earth conference whose result would be a massive united army the Cybermen couldn't overpower. The Cybermen on board,upon noticing the doctor's protective instincts to save Tegan elect to keep Briggs and her crew aboard to observe their reactions. The doctor evacuates Scott and Tegan back to the TARDIS as they face off Cybermen attempting to invade it's systems following Tegan attempting an emergency launch. Adric shrugs off the Briggs offer to join her,Scott's expedition and the freighters crew in an escape pod as the TARDIS gives chase-believing he can stop the ship through his own calculations. Meanwhile the warp device the Cybermen install sends the freighter backward in time 60 million years-still on course to Earth and just in time to become the source of destruction for the dinosaurs. After using the gold star Adric gave the doctor to disrupt the Cybermen's circuits to buy time the TARDIS attempts to pursue to kamikaze freighter to rescue Adric but they are too late. Adric is destroyed along with the freighter before a shocked doctor,Tegan and Nyssa.

                  One of the main themes of this story ends up being what I've heard referred to as a pre-destination time paradox. While Adric's surprisingly self sacrificing death did halt the Cybermen's plans to destroy Earth in the future,it resulted in the destruction of the highly successful dinosaur race whose extinction was part of Tegan's own history. Seeing as they hadn't been on Doctor Who for nearly a decade at this point,another important element of this story was that non of the characters outside the doctor had any awareness of the Cybermen. Professor Kyle's expedition were so intent on finding their lost mates,and Captain Brigg's freighter crew were so internally quarrelsome they both suspected the doctor and his equally unknowing companions of their missing/murdered crew before learning to trust him. These complexities are lost on the Cybermen,who only view emotions as a weakness to be exploited. That plus the surprisingly gripping sacrifice of Adric make this one of Doctor Who's most meaningful action stories that views the intensity of emotion from the Cybermen's outsider perspective.