Zygons, a shape-shifting alien race, and humans live in peace together on earth, but a group of rogue zygons threaten the peace between humans and zygons.
The fragile peace between the Humans and the Zygons is on a knife edge. Tensions run high as factions within the Zygon community seek to incite violent action against Humans. Called in by UNIT, the Doctor and Clara fight to bring the situation under control. But one question remains: Where on Earth is Osgood?