The Fourth Protocol is a 1987 Cold War spy film starring Michael Caine and Pierce Brosnan, based on the novel The Fourth Protocol by Frederick Forsyth.
The plot centres on a secret 1968 East-West agreement to halt nuclear proliferation. One of the clauses, the Fourth Protocol, forbids the non-conventional delivery of a nuclear weapon to a target.
MI5 agent John Preston (Michael Caine) breaks into the residence of British government official George Berenson on New Year's Eve and finds a number of top secret NATO files that should not have been there. He reports his findings to high-ranking British Secret Service official Sir Nigel Irvine (Ian Richardson), who deals with the leak. However, Preston's unauthorized action has embarrassed the acting-Director of MI5, Brian Harcourt-Smith (Julian Glover), so as punishment for his insubordination, Preston is relegated to lowly "Airports and Ports".
Meanwhile, KGB agent Major Valeri Petrofsky (Pierce Brosnan) is sent on a mission to England...