The Tyrants Tomb (Trials of Apollo 4)

There he meets Raphael, a priest around whom the villagers spin unsettling stories of impossible disappearances, cursed woods, and living stone. Merrick must separate truth from fairy tale, and gradually he realizes that Raphael is the key to a legacy left by generations of Tremayne explorers before him, one which will prove more valuable than quinine, and far more dangerous.