The Weeping Angels - Lonely assassins, they were called. No-one knows where they came from. They’re as old as the universe, or nearly. They’ve survived this long as they have the most perfect defence system ever evolved. They are quantum-locked. They don’t exist when being observed. The moment they’re seen by any living creature they freeze into rock. It’s a fact of their biology. In the sight of any living thing, they literally turn to stone. And you can’t kill a stone. Course, a stone can’t kill you either. But then you turn your head away, then you blink, and oh, yes, it can! Don’t take your eyes off that! That’s why they cover their eyes. They’re not weeping, they can’t risk looking at each other. Their greatest asset is their greatest curse. They can never be seen. The loneliest creatures in the universe.