The Weeping Angels are a powerful predatory species in the revived series of Doctor Who, serving as recurring enemies for the Eleventh Doctor after a one-shot appearance in the run of the Tenth. They have the ability to move at an almost unbelievably fast pace, but can only do so when no one looks at them due to a quantum lock that activates directly when they are observed. When someone sees them, they are forced to revert to a stone statue in the likeness of a winged humanoid.
They tend to gather in small groups, draining the energy from light fixtures to avoid being spotted by their preferred prey, sapient beings. When they capture a target, they send it through space and time, converting every second that the target stays in the displaced time period into food. The target is not harmed by this transfer, and in fact often lives the rest of their life rather peacefully in their new time period. Due to this, the Doctor has called the Weeping Angels "the only psychopaths in the universe to kill you nicely."
Weeping Angels and the PPC
Three Weeping Angels were carried into Headquarters when dimensional bleeding during the 2013 Blackout dropped a section of the building that they were lurking in into HQ's hallways. Agents Amelia Keaton, Ian Nahinu, and Gaspard De Grasse were the first to see them, and understandably absconded as fast as they could. The Weeping Angels had the run of the place until a destabilized plothole pulled the Doctor's TARDIS in as well.
Two of the Angels attacked Agents Christianne Shieh and Eledhwen Elerossiel, who had met up with the displaced canon character, but were defeated by Captain Dandy and the Department of External Security.
The third was encountered and subsumed by Slorp, which caused the aberration to grow wings as well as develop a version of the Weeping Angel's power set. These powers were weakened as the Angel was digested, and vanished entirely after Slorp was blown up and forced to reform itself.