Investigating the disappearance of an eminent scientist, the Doctor and his companions follow his trail to the London headquarters of International Electromatics, a global supplier of electronic equipment run by the formidable Tobias Vaughan. Teaming up with the newly formed United Nations Intelligence Taskforce (UNIT) under the command of Brigadier Lethbridge-Stewart, the Doctor soon suspects that Vaughan is working to his own sinister agenda. As Cybermen invade in cities all over the world, can the Doctor convince Vaughan to help him defeat their plan for global domination?