Used book – SANS ATOUT DANS LA GUEULE DU LOUP, Pierre Boileau, Thomas Narcejac, Daniel Ceppi

During an excursion in Auvergne, Sans Atout and his friend Paul discover a man left for dead... Their investigation leads them into a vast network of underground tunnels infested with bats, where the Beast seems to reign. The two boys are sure they saw it and even heard its dreadful cry. But other monsters, human ones this time, will stand in their way. Strange machinations are afoot underground. For ages 9 and up.