The murder of a prostitute, who was also a German agent, in German-occupied Warsaw in 1942 causes Major Grau of the Abwehr to start an investigation. His evidence soon points to the killer being one of three German generals: General von Seidlitz-Gabler; General Kahlenberge, his chief of staff; or General Tanz. Grau's investigation is cut short by his sudden promotion and transfer to Paris at the instigation of these officers. The case in Warsaw remains closed until all three officers meet in Paris in July 1944. Paris is then a hotbed of intrigue, with senior Wehrmacht officers plotting to assassinate Adolf Hitler. Kahlenberge is deeply involved in the plot, while von Seidlitz-Gabler is aware of its existence but is sitting on the fence, awaiting the outcome. Tanz is unaware of the plot and remains totally loyal to Hitler. On the night of 19 July 1944, Tanz orders his driver, Kurt Hartmann, to procure a prostitute; Tanz butchers her so as to implicate Hartmann, but offers Hartmann the chance to desert, which he accepts. When Grau, who is now a Lieutenant Colonel, learns of the murder, committed in the same manner as the first, he resumes his investigation and concludes that Tanz is the killer. However, his timing is unfortunate, because the very next day is the 20 Julyassassination attempt. While Grau is accusing Tanz face to face, word arrives that Hitler has survived, so Tanz kills Grau and labels him as one of the plot conspirators to cover his tracks. Jumping to 1965, the murder of a prostitute in Hamburg draws the attention of Interpol Inspector Morand, who owes a debt of gratitude to Grau for not revealing his connection to the French Resistance during the war. Almost certain there is a connection to Grau's 1942 case, Morand reopens the cold case, soon finding a link to the 1944 murder as well. Morand begins to tie up the loose ends: he finds no criminal activity from Kahlenberge or Seidlitz-Gabler, but learns of one manwho knew which man is the real killer. Morand confronts Tanz, recently released after serving 20 years as a war criminal, at a reunion dinner for Tanz's former panzer division. When Morand produces Hartmann as his witness, Tanz goes into a vacant room and shoots himself.
Both O'Toole and Sharif were hesitant to take on their roles for this film. Feeling they owed it to producer Sam Spiegel for making them international stars in Lawrence of Arabia, they did so anyway.