In 1906, Professor Alexander Saxton (Christopher Lee), a renowned United Kingdom anthropology, is returning to Europe by the Trans-Siberian Express from China to Moscow. With him is a crate containing the frozen remains of a primitive humanoid creature that he discovered in a cave in Manchuria. He hopes it is a Transitional fossil#Missing_links in human evolution. Doctor Wells (Peter Cushing), Saxton’s friendly rival and Royal Society colleague, is also on-board but travelling separately. Before the train departs Shanghai, a thief is found dead on the platform. His eyes are completely white and without irises or pupils, and a bystander initially mistakes him for a blind man. A monk named Father Pujardov (Alberto de Mendoza), the spiritual advisor to a Poles Count and Countess who are also waiting to board the train, proclaims the contents of the crate to be evil. Saxton furiously dismisses this as superstition. Saxton’s eagerness to keep his scientific find secret arouses the suspicion of Wells, who bribes a porter to investigate the crate. The porter is killed by the ape-like creature within, which then escapes the crate by picking the lock. The creature finds more victims as it roams the moving train, each victim being found with the same opaque, white eyes. An autopsy suggests that the brains of the victims are being drained of memories and knowledge. When the creature is gunned down by police Inspector Mirov, the threat seems to have been vanquished. Saxton and Wells discover that images are retained in a liquid found inside the eyeball of the corpse, which reveal a prehistoric Earth and a view of the planet seen from space. They deduce that the real threat is somehow a formless Extraterrestrial life that inhabited the body of the creature and now resides within the Inspector. Father Pujardov, sensing the greater presence inside the Inspector and believing it to be that of Satan, renounces his faith to pledge allegiance to the mysterious entity. News of the murders is wired to the Russian authorities. An intimidating Cossack officer, Captain Kazan (Telly Savalas), boards the train with a handful of his men. Kazan believes the train is transporting rebels; he is only convinced of the alien’s existence when Mirov is discovered to be the creature’s host when Saxton switches off the lights and Mirov’s eyes glow. The creature has absorbed the memories of Wells’ assistant, an engineer, and others. It seeks the Polish Count’s metallurgy knowledge too, in order to build a vessel to escape Earth. Kazan fatally shoots Mirov, and the alien transfers itself to the deranged Pujardov. The passengers flee to the freight car while Pujardov murders Kazan, his men, and the Count, draining all their minds. Saxton rescues the Countess and holds Pujardov at gunpoint. Saxton, having discovered that bright light prevents the entity from draining minds or transferring to another body, forces Pujardov into a brightly lit area. The creature/Pujardov explains that it is a collective form of energy from another galaxy. Trapped on Earth in the distant past after being left behind in an accident, it survived for millions of years in the bodies of protozoa, fish and other animals, but cannot live outside a living being longer than a few moments. The creature begs to be spared, tempting Saxton with its advanced knowledge of technology and cures for diseases. While Saxton is distracted by the offer, the creature resurrects the Count’s corpse which attacks Saxton. Saxton and the Countess flee the creature, but it now resurrects all of its victims as zombies. Battling their way through, Saxton and the Countess eventually reach the caboose, where the other survivors have taken uge. Once there, Saxton and Wells work desperately to uncouple themselves from the rest of the train. The Russian government sends a telegram to a dispatch station ahead, instructing them to destroy the train by sending it down a dead-end spur. Speculating that it must be war, the station staff switch the points. The creature takes control of the train as it enters the spur. Saxton and Wells manage separate the last car from the rest of the train just before the train jumps the track and tumbles to the bottom of a deep ravine. The caboose rolls precariously to the end of the track before stopping, inches away from the edge of the cliff. The survivors quickly depart from the van while Saxton, Wells and the Countess gaze over the ravine to witness the inferno consuming the train and its unearthly inhabitants.
