Doctor Who: Earthshock (TV)

In the 26th century, the Doctor, Adric, Nyssa and Tegan come to the aid of a platoon of soldiers, which is investigating the murder of a scientific team in a cave complex on Earth. The Doctor discovers that the killers are actually androids serving the Cybermen, and are guarding a bomb intended to destroy the planet. The Doctor disarms the explosive but by tracing the detonation signal, he learns that the greatest danger is yet to come. The Cybermen have secreted themselves on board a freighter heading for Earth, which will unknowingly serve as the bridgehead for a massive invasion.