Geronimo and his friends set sail to the Ratlapagos Islands to search for a sunken treasure. He soon begins to suspect that they aren't the only ones looking for the treasure.

Geronimo Stilton's ancient ancestor is back in another prehistoric adventure! A mysterious rodent has been shipwrecked on Mouse Island. He's a prehistoric pirate, and he's searching for a lost Stone Age treasure! Geronimo Stiltonoot and his family volunteer to help him on his dangerous hunt. Petrified cheese! Can they find the treasure without going extinct on the way?