According to Michael Caine's auto-biography "What's It All About?" (1992), Caine said of his role, the "part had originally been given to James Caan and he had dropped out at the last moment, I had to finish Water (1985) on the Friday night, and whizz off to Berlin to start filming on the Monday morning. It all happened so quickly that I didn't even have time for a wardrobe fitting and wore my own clothes in the movie. Even more to the point, I didn't have time to read the script properly, and only too late did I realize that I couldn't understand the plot, so God help the poor audience who would eventually see it".
Michael Caine replaced James Caan. Caan walked off the production the day before filming started. John Frankenheimer had to film around his absent lead character until Caine was hired as a replacement. With time on his hands, Frankenheimer shot extra footage of the assassins in the Geneva ferry scene.
John Frankenheimer admitted to having a crush on Lilli Palmer when she was appearing on stage in "The Four Poster" in the 1950s and returned to see her numerous times in the play. He confessed his youthful infatuation to her when they worked together on The Holcroft Covenant (1985) and complimented her beauty despite the actress being in her 70s at the time.
Director John Frankenheimer had Michael Caine use a remote to access the calls on the answering machine, despite the fact that no such device has ever existed. Frankenheimer explained that it freed the actor to be able to move around the room.
Second ever feature film adaptation of a Robert Ludlum novel and the third Ludlum adaption overall for any filmed production. The Osterman Weekend (1983) had debuted in theaters in 1983 whilst The Rhinemann Exchange (1977) had been made for television in 1977. The picture was the second of three 1980s features based on Ludlum novels, the decade ended with a tele-movie of The Bourne Identity (1988).
According to the book 'Onscreen and Undercover: The Ultimate Book of Movie Espionage' (2006) by Wesley Britton, "[Michael] Caine didn't like the film. He signed on because the director was to be John Frankenheimer, the man behind one of Caine's favorite films, The Manchurian Candidate (1962)...At first, James Caan was to play Holcroft but pulled out at the last minute. Caine was in wardrobe [sic] before he ever saw the script, which he found incomprehensible".
The film's opening scenes, set during the end of World War II, were shot in black-and-white, unlike the rest of the movie which was filmed in color. The black-and-white opener reflected newsreels of the era, the sequence also featuring some original b&w archive footage of a battle, which was inter-cut with the movie's bw filmed footage.
This 1985 movie featured a character called Herr Oberst (Richard Münch) whose codename was "Oberst" which is a German word which translates from the German language as "Colonel". Coincidentally, released also in 1985 was the German film Colonel Redl (1985) whose original title was "Oberst Redl".
The trivia item below may give away important plot points.
Michael Caine stars in this espionage movie where the story-line develops to reveal a scheme by neo-Nazis to establish "The Fourth Reich". One of Caine's next two spy pictures released in 1987 would be called The Fourth Protocol (1987).