They monitor the afterworld and work for The Fates. They are either born Angels and some are dead supernaturals.
They can look in the eyes of a person and get a vision of past events that that person has witnessed. Although they are generally forbidden to administer justice to living beings, they can intervene directly if they act in direct investigations of the Fates.
They can conjure a big sword, the Sword of Justice, which causes severe agony even on ghosts, who normally feel no pain.
There are three generations of Angels. After the first 'batch' of Angels became too far removed from humanity to effectively carry out their tasks, they were reassigned to higher tasks and a 'second generation' was created. When these Angels too became too detached from their wards, the concept of Ascended Angels was instituted, where dead supernatural ghosts could be 'promoted' to Angelhood.
Faith or good behaviour was not paramount in the selections as The Fates has a penchant for picking just those ghosts that had something new to add to the mix. Eve Levine was chosen for her dark side, as she knew like no other to think like the beings she hunted.