In 1859, ex-smuggler Merrick Tremain lies in his sprawling estate in Cornwall recovering from a serious injury. Strange things begin to happen, he sees trees explode and statues begin to move, his brother insists Merrick is losing his mind. Eager to get away from home Merrick excepts a job from the East India Company, where he will travel to the Amazon to obtain quinine. Merrick knows this is an insane idea, he can barely walk, but he needs to get away and prove that he is not going mad. In a tiny town in the Amazon things get even worse. There is a line in the sand made of salt and anyone who crosses it is killed by something living in the forest. Merrick begins to wonder if he truly is losing his mind but desperate to prove there is something else going on, he sets out to discover what happened to the expeditions that came before him and is particularly intrigued by the young priest Raphael who claims to have known Merrick’s grandfather in the same tiny Amazonian town decades before.