Don Siegel took over the directing chores from Peter Hyams on this taut cold war action film, based on the novel by Walter Wager. With the cold war between the United States and the Soviet Union thawing, old KGB hard-liner Nicolai Dalchimsky (Donald Pleasence) activates a group of Americans who were brainwashed twenty years earlier to blow up United States defenses when a passage from a Robert Frost poem is recited to them. When bombs go off at an abandoned United States defense installation, the Kremlin realizes that they have a rogue KGB agent on their hands who is trying to re-ignite the cold war. To stop him, the Russians send out KGB agent Grigori Borzov (Charles Bronson). Accompanying him is KGB double agent Barbara (Lee Remick). As the two agents try to stop Nicolai from starting World War III, they find time to fall in love with each other.
~ Paul Brenner, All Movie Guide