One day, a letter is dropped off at Solange's residence addressed to her husband, Bernard. Curious to know its contents, she discreetly opens it, only to discover that due to her spouse's paraplegia, they are requesting that a reliable replacement be sent in his stead to oversea the newly finished railroad that has been built in the Congo. Reading this brings back fond memories for Solange, who recalls the times when she cheated on her husband with several lovers while traveling alone. Furthermore, it reminds her that she has never been able to indulge her craving to hunt wild animals.
Solange manages to convince Bernard to let her go as the representative, and he gives her a necklace with a hyena tooth on it as a good luck charm. Enthused, the wife also manages to persuade Bernard's daughter (and her stepdaughter) Cosetta, to join her on the trip. The stepmother knows that both she and Cosette are the sole heirs to Bernard's fortune, and as such, thinks to herself how lovely it would be if the child were to turn up "missing" in the Congo.
The two eventually reach the African railroad, joined by an armed escort. Once the train starts rolling, the overzealous Solange begins firing her rifle at every animal she sees, killing vultures, a lion, and eventually a rhinoceros. Recalling that getting a rhino horn in hopes of curing Bernard's impotence was the primary excuse that she had given for wanting to go on this trip, she sends several men out to obtain it. However, they are quickly ambushed by members of the Bantu tribe, who are enraged that whites continue to poach animals from their land.
One of the men on the train warns the two Lannoy women that the tribe is particularly aggressive this time because they know that there are white women on board. He further clarifies that the Bantu sacrifices such women at rituals where the tribal women drink their blood and the tribal men eat their flesh. This gives Solange an enticing idea. She tells the men that she's taking Cosette into a different car, so that they may hide. In reality, however, the stepmother knocks the girl unconscious with her rifle and throws her off the train. Just as the woman had hoped, several Bantu members spot her stepdaughter and take her away.
Days later, Solange is stunned to see that the girl has returned safe and sound, and accompanied by a male Bantu. Cosette explains that the man, Nkuomu, took it upon himself to return her after the village Shaman halted the sacrifice ritual. Unbeknownst to the girl, this was because she was wearing the hyena tooth, which her stepmother had passed over to her.
Solange is distraught that her plan had failed, but that night, manages to concoct another. She strangles the sleeping Cosette to death, and then runs to fetch Nkuomu. When the Bantu man arrives, Solange stabs him in the back with a dagger, and then positions his corpse to make it look like he was raping Cosette. Her ruse manages to fool the escort men, and three weeks later, she returns home to Rochefort.
Solange uses several onions to force herself to cry, and then tells her husband "what happened". Unexpectedly, Bernard shoots her in the chest with a handgun. As she lies dying, the man presents a second hyena tooth and gives his explanation. He states that he was once rescued from a giant python in the Congo by the Bantu tribe. The shaman, Umumba, then agreed to treat his mortal wounds in exchange for the promise that he remove his railroad project from their territory. A man of his word, Bernard did just that, and as a show of thanks, Umumba presented to him the two magically enchanted hyena teeth. Some time later, after reading a book about the Bantu, he learned their secret. One tooth can act as an audio transmitter if the other one is pricked to the user's skull. Wanting to test it out, and suspicious of Solange's behavior, he hid one tooth in her clothing and learned of her adulterous affairs, long before her trip to Africa.
Bernard adds that even he could have never predicted that her obscene wickedness would extend to murdering his only and completely innocent daughter, and then shoots her once again between the eyes, before finally turning the gun on himself.