They can be activated only by a special code phrase, a line from the Robert Frost poem "Stopping by Woods on a Snowy Evening" – followed by the agent's real first name.

Nikolai Dalchimsky, a rogue KGB headquarters clerk, travels to America and takes with him the Telefon Book, which contains the names, addresses and telephone numbers of all the sleeper agents.

KGB Major Grigori Borzov, who was selected in part for his photographic memory, memorizes the contents of the only other copy of the Telefon Book and is sent to find and stop Dalchimsky quietly, before either side learns what is happening and possibly starts a war.

Eventually, Borzov realizes the method behind Dalchimsky's pattern of attacks: he has chosen the agents by the first letters of their American hometowns by "writing" his own name in sabotage across America.

"[8] The city skyline depicting Houston, where part of the story line occurred, is actually that of Great Falls, Montana, where the majority of the film was shot.

The present day Paris Gibson square was undamaged, but the explosion started roof fires on a couple of nearby houses that were quickly extinguished by city firefighters hired by the movie company on stand by.

The scenes with fires and explosions at a rocket engine test site were filmed at Rocketdyne's Santa Susana Field Laboratory in the mountains northwest of Los Angeles.

According to director Siegel, actress Lee Remick was terrified of Charles Bronson, and when asked to touch his face during a scene, responded, "I don't dare.

[12] Vincent Canby of The New York Times wrote, "Though there are action sequences in 'Telefon,' they are never sustained, and the screenplay only occasionally comes up with witty substitutes for the missing plausibility.

"[13] Arthur D. Murphy of Variety called the film "pleasant escapism" with a story that "runs its interesting if predictable course until fadeout romantic clinch as the stars tell their respective employers to let them live in peace somewhere nice and idyllic, which by this time is really asking too much of audiences.

"[14] Gene Siskel of the Chicago Tribune gave the film 3 stars out of 4 and wrote that it "is by no means a great picture — just solid action held together by a string of explosions.

"[16] Gary Arnold of The Washington Post stated, "The real problem is that the filmmakers lay out this story blueprint so doggedly that the audience is invariably 25 pages of expository chitchat ahead of them.

"[17] Richard Combs of The Monthly Film Bulletin wrote, "This dismal attempt to ring some changes in the spy genre—the protagonist is a KGB agent, his mission is to preserve East-West cordiality—is fatally undercut both by its surprisingly lukewarm plot and unengaged characters and by the fact that its updating is already out of date, Russian-American détente having sprung many leaks.

But those right hands definitely didn’t belong to old fart Siegel, who blew the picture’s chance for success by de-emphasizing the kooky elements and emphasizing the dull ones.