The Doctor, Amy and Rory are awe-struck by their first sight of "Hope Eternal", a super-earth bigger than Earth itself with heavy gravity, volcanoes and a crust loaded with mineral deposits. But their wonder is cut short when they discover a body dumped on the ground — a huge figure with extraordinarily long arms covered in thick, purple scales. Yet the corpse is not alien: he's human, albeit unlike any human Amy and Rory have ever seen. The Nu-Humans have adapted their genes to fit their new environment, and formed a thriving colony. But now they are facing a terrible threat. Can the Doctor find out who is killing Nu-Humans and why — before he, Amy and Rory are themselves tried for murder?