In 1859, ex-East India Company smuggler Merrick Tremayne is trapped at home in Cornwall with an injury that almost cost him his leg. When the India Office recruits him for an expedition to fetch quinine --- essential for the treatment of malaria --- from deep within Peru, he knows it's a terrible idea; nearly every able-bodied expeditionary who's made the attempt has died, and he can barely walk. But Merrick is eager to escape the strange events plaguing his family's crumbling estate, so he sets off, against his better judgment, for the edge of the Amazon.

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 that will prove more valuable than quinine, and far more dangerous.