My Brother-in-law Killed My Sister

At a formal ceremony, anthropologist Étienne Sembadel honors his co-worker Octave Clapoteau. Esther Bouloire approaches them and insists that they dine together, revealing that she suspects her sister Genevieve was murdered and her body burned. The scholars dismiss her claims as crazy and arrange for her to be admitted to a mental health clinic.

Upon her release, Esther is accompanied by Sembadel and Clapoteau as she races to her veterinary practice and then to the office of her late father's law business, where she demonstrates her sister's house and Muriel's house. She explains the Bouloire Brothers' business and describes the recent, mysterious deaths of the men and their wives. She points to Jocelyn, the hunchbacked third brother, as the likely orchestrator of these events.

The academics visit Esther's brother-in-law, finding him eccentric but harmless. They decide to press on and visit Jocelyn Bouloire-Haussmann, hoping to learn more about Genevieve. Jocelyn claims Genevieve ran away and dismisses the Munoz lead as dead weight.

Less than two hours after the Jocelyn visit, Clapoteau's Roman lover, Countess Renata Palozzi, is beaten by thugs, escalating the danger around the Bouloire family. The academics grow suspicious of Jocelyn's role, and they angrily confront Esther, only to be rebuked for visiting him without invitation.

Jocelyn calls Sembadel to say that Genevieve was fond of a Swiss lawyer named Bongrand. Sembadel and Clapoteau fly to Geneva, where Bongrand says he does not know Genevieve but suggests she may have known his son, Paul Bongrand Jr., who died in a climbing accident in the Dolomites a fortnight earlier. Soon after, the police arrest the two academics on suspicion of Bongrand Jr.'s death.

Back in France, Viscount Homecourt seeks Muriel's help but instead warns Esther that three killers are after him because Jocelyn claimed he had revealed Munoz's name. He admits that he and many others were responsible for Munoz's murder but insists he does not know where Genevieve has gone. Esther ejects him from the house, and he is shot dead as he passes the driveway gate.

Three days later, Jocelyn approaches Sembadel's wife with the accusation that Esther and her husband are responsible for Homecourt's death. Mrs. Sembadel throws him out, deepening the rift within the family.

The two academics are run off the road by a car, a warning that heightens their resolve. They publish an exposé in Left-Weekly detailing twelve murders connected to the Bouloire affair, naming a chain of victims tied to the family's intrigue.

Esther presents journalists with documents found in her sister's safe that incriminate 41 people, including three ministers. She confronts Jocelyn, whose advisor warns that the revelation could embarrass him and jeopardize his position.

The next day, Muriel is killed by three assassins as she leaves the Bouloire-Haussmann offices. Esther and Muriel's husband Leon retrieve Sembadel and Clapoteau from their apartment, but Leon is shot by assailants on his way home.

They travel to the Countess Renata Palozzi's chateau, only to find it burned. They pursue the Countess to Rome, where she arranges safety for the four of them. Moments after receiving this guarantee, Sembadel and Clapoteau are gunned down near the Vatican.

The film ends with Sembadel and Clapoteau dancing together in Heaven, a surreal coda after their violent fate. The final image lingers on their peaceful ascent amid the chaos of the world they left behind.