Beginning with the defection of KGB agent Yul Brenner, his information to the Americans (and namely Fonda) sets in motion the devious wheels of "Le Serpent". His intel- that there are highly placed spies in all echelons of governments around the world- kick starts a series of murders, wearisome eyes and urgent secret memos in both France and America. Philippe Noiret is one such agent cast under suspicion. British officer Dirk Bogarde, seemingly with his fingers in every cookie jar, plays both sides. Fonda is unsure of Brenner's real intentions. And all the while, bodies of agents turn up dead, others go missing and seemingly innocent photographs belie sinister intentions. All of this is handled in Verneuil's no-nonsense approach, refusing to telegraph anyone's actual motive and creating a paranoid atmosphere where anyone could be "le serpent" working their magic to eradicate the others.
I can't see "Le Serpent" existing in any other time period than the 70's. Echoing the later American thrillers of Sydney Pollack and especially Alan J. Pakula, "Le Serpent" is an arid exploration of the callowness involved in world politics. The basic sentiment of wanting our world to be safe, but not knowing just exactly how we make it so safe, continually runs through the veins of this film. It's a thriller, yes, but also a pretty frightening document of plausible denialability.