Commandant Michel de Palma, known by his colleagues as 'the Baron', has chosen early retirement and plans to travel the world. But he is dragged back into the force when a case that has haunted him for a decade erupts once more.

Resurfacing from Le Guen's Cave, a prehistoric grotto thirty-eight metres below sea level outside Marseilles, France, an experienced diver mysteriously gets into difficulties. Meanwhile, Thomas Autran, a serial killer with a peculiar interest in the supernatural, suffering from a dangerous form of schizophrenia, is once again on the run.

Ancient cave paintings, savage murders committed according to a precise ritual: a return to the first ages of humanity, the era of the great Palaeolithic hunters. And despite the gory trail left at each crime scene, de Palma must first understand the child, the secrets of a family, a story of exploitation - and revenge - before he can track down the First Man.