This movie was made and released about four years after its source novel of the same name by Noel Behn was first published in 1966. This was the first ever adaptation for cinema of a work by Behn. The only other one is The Brink's Job (1978) based on Behn's book 'Big Stick Up At Brink's'.
Utilizes an innovative technique: scenes spoken in Russian begin in Russian and after a couple of interchanges segue to being spoken in English, avoiding either usual extreme of subtitling or dubbing into English.
Ward: I don't know what they taught you in the classroom about intelligence and espionage. Everything I know, I learned on the street, but I can assure you of one thing: It has no size, no shape and no rules. At the very best it's what you least expect so you've gotta be ready for anything.
Ward: Now look, I think we've left no stone unturned. But let's not kid ourselves. If any of us is caught there's only a remote possibility we'd be mistaken for Russians. Keep in mind that close examination takes time, and that time they use on you could let the rest of us escape.