Alexander Saxton (Christopher Lee), a brilliant British anthropologist researching in the Russian Far East, boards the Trans-Siberian Express with his latest discovery, a frozen specimen he hopes to prove is the missing link. But en route to Europe, passengers begin to turn up dead, and terror engulfs the train as Saxton and his partner, Dr. Wells (Peter Cushing), struggle to contain a mysterious -- and increasingly murderous -- force with the power to control minds.