They were like birds. Large, black birds – shadowy descendants of pterodactyls – gathered in the shadows and out of sight. A movement from one of them could be dismissed as a trick of the light – the mind placing tricks with the shadows of the night. They were hungry. Ravenous. And they could feel their next meal getting close. A rip in time. Juicy energy waiting to be consumed. Gathered around one special person. A person with the potential to change the world. All they had to do was find a way through and then they could begin their feast.The Doctor takes Clara to Edinburgh where he has to plug up a leaking energy well. Unfortunately, he is already too late and they have to pursue the shadowy bird-like creatures through time to stop them consuming the raw energy of a child destined for great things...