British spy John Preston (Michael Caine), recently demoted by his boss for a well-intentioned but unsanctioned mission, stumbles onto a covert plot by KGB agent Valeri Petrofsky (Pierce Brosnan), who is attempting to build and detonate a nuclear bomb on British soil and blame it on the Americans. With the support of the ailing MI5 director, Preston, who is still at odds with several of his superiors, attempts to uncover and thwart the plot before it's too late.