Clint Eastwood was given a copy of the 1966 novel by producer Jennings Lang, and was engrossed throughout the night in reading it. This was the first of several films where Eastwood agreed to storylines where nubile females look at him adoringly (including minors in this film and "Pale Rider"). Eastwood considered the film as "an opportunity to play true emotions and not totally operatic and not lighting cannons with cigars". Albert Maltz was brought in to draft the script, but disagreements in the end led to a revision of the script by Claude Traverse, who although uncredited, led to Maltz being credited under a pseudonym. Maltz had originally written a script with a happy ending, in which Eastwood's character and the girl live happily ever after. Both Eastwood and director Don Siegel felt that an ending faithful to that of the book would be a stronger anti-war statement, and Eastwood's character would be killed. The film, according to Siegel, deals with the themes of sex, violence and vengeance, and was based around "the basic desire of women to castrate men" though the central theme was the impact of a man having sex with multiple woman.