The Amazon rainforest, 1827. The Doctor, Amy and Rory arrive in the jungle near a hurriedly abandoned campsite, where they are surrounded by hungry black caiman — huge lizards. Only the arrival of a man with a rifle sees off the giant beasts. Oliver Blazington has come to the forest to bag big game, and his companion Garrett is a naturalist, collecting exotic creatures for London Zoo. But the Doctor soon discovers that another very different hunter is stalking the Amazon. Animals and people have been disappearing without trace, and local villagers speak darkly of "the Eye of the Jungle". Amy senses that the all-seeing Eye is watching them — but she and Rory are powerless to intervene when it sets its sights on the Doctor...