Édouard Marlaud, a zoologist, leaves his Natural History museum to go on an expedition to the Congo. He wants to find proof of the existence of a legendary monster, the Mokélé-Mbembé. Once he arrives in Africa, he plunges into the jungle surrounding the tributaries of the Congo.

There, he photographs wildlife and despairs that he will never see the Mokélé. However, the fearsome creature is indeed there, very close by! But, every time, the zoologist takes it for another animal : when he sees its legs, he thinks he’s seeing those of an elephant, its tail becomes a snake, its body becomes the body of a hippopotamus…