Moreau, Jean-Pierre Melville, a reporter for Agence France-Presse (AFP), is asked by his editor to find out why Fèvre-Berthier, Paula Dehelly the French delegate to the United Nations, did not attend that day's meeting of the General Assembly. Moreau talks to McKimmie, an information officer at the UN, who does not know anything, but mentions Fèvre-Berthier's family is also trying to find the diplomat, and then Fèvre-Berthier's secretary, who suggests he may be with a woman, but does not know who or where.
At a dead end, Moreau asks his friend Delmas, Pierre Grasset an alcoholic tabloid photographer, for help. Delmas has taken pictures of Fèvre-Berthier with three different women who are not his wife, so Moreau and Delmas set off to find out if Fèvre-Berthier is with one of them. They visit Judith Nelson, Ginger Hall, a stage actress, between the acts of a Broadway play at the Mercury Theater, Virginia Graham, Barbara Hall, a jazz singer, at a Capitol Records recording studio, and Bessie Reed, Monique Hennessy, a burlesque dancer, at the Ridgewood Rathskeller, and even talk to Gloria, Glenda Leigh, a high-end call girl who "specializes in diplomats", at a French-Chinese-themed brothel, but do not find Fèvre-Berthier.
Dejected, they go to a diner, where they hear on the radio that Judith slit her wrists just after they left her.
Moreau and Delmas go to the hospital and manage to sneak into Judith's room. She tells Moreau that she tried to kill herself because she loved Fèvre-Berthier, but he is dead. When she begins to become hysterical and does not want to say any more, Delmas demands to know where Fèvre-Berthier is and how he died until he learns that Judith had found the diplomat dead in her apartment, presumably of a heart attack.
After taking a picture of Judith, Delmas steals her keys, and he and Moreau go to her apartment, where they find Fèvre-Berthier's corpse sitting up on a sofa. While Moreau calls his boss to give an update, Delmas moves the body to the bed so he can take a picture that will sell for more money, which shocks Moreau. Rouvier, Jean Darcante comes to the apartment and tells Delmas that Fèvre-Berthier was a hero of the French Resistance and it will not be reported that he died in the apartment of his mistress. Unmoved by Rouvier's story, Delmas reluctantly gives Rouvier a roll of film after Moreau indicates he intends to take the pictures by force. The three men put Fèvre-Berthier in Rouvier's car and leave it to be found there.
Incensed, Delmas tells Moreau that he intends to recoup some of his losses by getting a picture of Fèvre-Berthier's wife right after he tells her that she is a widow. Moreau comes along so he can at least tell the woman gently, but, before he can say anything, Anne Fèvre-Berthier, Christiane Eudes the diplomat's daughter, enters and asks her mother to leave the room. Anne has been following Moreau since he left McKimmie's office, hoping he would lead her to her father. She knows about Fèvre-Berthier's affair with Judith, but says her mother does not.
Delmas abruptly runs away, and Moreau and Anne chase him. Realizing Delmas gave Rouvier a decoy roll of film, Moreau looks for Delmas at a photo lab, his apartment, and the offices of various newspapers and magazines. After searching for two hours, Moreau figures Delmas has probably already sold the pictures and will be celebrating with a drink at the Pike Slip Inn. He and Anne go there and find Delmas, who is very intoxicated. Moreau punches Delmas and leaves, and Anne, tears in her eyes, exchanges a look with Delmas before following.
Staggering out into the early-morning light, Delmas decides not to try to drive and begins to walk. He passes a storm drain and, after some consideration, pushes two rolls of film through the grate. As he walks away, he laughs to himself.
