The world, unknown to man, plays host to a variety of magical creatures. The most powerful of which are the Immortals: earthbound Angels and Demons. The Immortals have been at war since man was young, both sides bound and governed by a set of strict rules known as the Immortal laws.
Gabriel is an Immortal, lost into the world of man, completely ignorant to the magical world around him. Never knowing his real parents he is brought up by a hired nanny in the penthouse of one of London's most expensive hotels.
Gabriel and his sister get dragged into a bank robbery and as a result Gabriel is thrown head first into the magical world, catalyzing a string of bizarre capabilities Gabriel never knew he had- namely incredible healing and the ability to grow white feathered wings on demand. He comes to the realization that he is an Angel. The strange events surrounding Gabriel and Molly's survival of the bank robbery make him famous and so is brought to the attention of the Immortals. Unfortunately for Gabriel that means Demons too.
Barely escaping an attack from a scorned Demon and his Spawns, being arrested by an overly suspicious cop he is saved by the Angels, specifically his Aunt Bethany. Bethany takes Gabriel back to her home at 'The Institute' - an underground society of Angels, deep below London, dedicated to the eradication of Evil.
Gabriel is keen to help fight against The Institute's latest enemy. However, this is enemy is unlike any The Institute has seen before because this enemy is not a Demon, it is an Angel gone rogue. An Angel hell-bent on executing his own brand of law on those who he deems to have sinned. He does this through means of twisted and ironic games that he calls the Justice Games and after the Angel kidnaps a whole prison of convicts it seems he now has an unlimited amount of sinners to play with.
However, all is not as it appears as Gabriel finds out after his first mission with The Institute he the Immortal world, Demon and Angel alike, when an explosion that should have burnt Gabriel alive leaves no mark. This specifically Demon characteristic leaves Master Nevaeh, the head of The Institute, baffled.
A consultation with The Institute's most powerful, all be it mad, psychic raises even more questions. With all this uncertainly Master Nevaeh evicts Gabriel from the Institute.
Made into an outcast Gabriel is unsure what to do when he uncovers an elaborate plot made by the Demons. The rogue Angel is being manipulated, the end game that he will unknowingly break the most important Immortal Law: An Immortal can't murder and Innocent. If broken by an Angel, the Law dictates that Lucifer can freely enter Earth.
After The Institute is blown up, trapping every Angel miles below London Gabriel realizes that there was more reason behind his eviction than it had appeared and now it is up to Gabriel to use his unique gifts to track down a dark lost relic that prophecy states is the only way to save the world.