Penryn, her wheelchair bound sister Paige, and her mother are trying to escape from gangs who are taking over the neighborhood they are staying in (I picture it being kind of like a bombed out city setting). Apparently angels have destroyed everyone and everything they can find on Earth, although we never find out why.
As the family is trying to escape, they come across a group of angels attacking another angel. The angels are cutting off the lone angels white wings. They try to sneak around but the other angels hear and come after them, so to distract them Penryn throws the lone angel his sword and he fights back, chasing the other angels away. Before they leave however, one of the angels grabs Paige and takes off with her.
Penryn takes the broken angel from the street (along with his cut wings) to a safer place and begins to mend him to try to get info about where they would have taken her sister. In the meantime, we learn that her mother is schizophrentic and has taken off on her own, along with learning that she was the one who caused Paige to be in a wheelchair by hurting her during one of her episodes.
They are attacked by a gang but fight their way out of it, and Penryn tells the angel (who's name is Raffe) that since she saved him he owes her the courtesy of helping her find her sister. Although they are enemies he agrees.
They are captured on the road by what they think is just another gang, but then once imprisoned they talk to the leader, Obi, and it turns out they are a resistance movement against the angels. Penryn is overjoyed to find out the populace are beginning to fight back, but they must still try to escape so that A)no one finds out Raffe is an angel, and B)so that Penryn can go to the aerie to find her sister.
They escape once but are captured again. They are put to work to help out the camp, and this is when Pen meets Tweedledee and Tweedledum (not their real names, but they ARE twins). They challenge Pen to get into a fight with a "popular" girl they don't like since she kicked a guard's butt earlier for trying to touch her. It turns out fights are allowed to go on and people in the camp make bets because it's the only way to let off steam while stuck there.
Pen starts to decline, but then they tell her if she does it they will help her get away so she can go find her sister. She gets into the fight, but there is a crazy commotion outside and it's cut short. Pen and Raffe escape during the fray, but it turns out something small has been killing people and tearing them to shreds. They have small teeth marks all over them, and no one knows what it is unless it's some wild cannibal kids, so they start calling them "low demons".
Pen and Raffe reach the aerie by Pen dressing herself up in a slutty outfit to gain entrance into the stronghold. They allow her through and once inside Raffe bandages his wings to his back to make it seem like they aren't cut off so the other angels don't think he's fallen.
Raffe tells her to go up to this albino angel (Josiah) and talk him into going to the bathroom to meet Raffe where no one will hear them. When she gets up to him, she sees that the reason he is offset from the other angels and their human women is that he has blood red eyes. She spills a drink on him, and when he heads to the bathroom she and Raffe follow him in.
It turns out Raffe rescued Josiah and was his military leader and trainer so Josiah tells them that since Gabriel the Messenger has been killed by humans there is unrest among the angels over who will take his place, and some are saying they want Raffe, who's real name is Raphael (an archangel), to be the successor, but another angel with ties to Hell is trying to take it, along with an angel in cahoots with the Hell angel (who Pen calls the Politician).
Raffe begs Josiah to get his wings sewn back on and Josiah agrees. I honestly can't remember the girl angel's name, I think it's Raelynn or something like that?
While Pen is waiting for Raffe to come back from his surgery, she sees that Dum is one of the waiters at this place, and gets him to help her get a servant's uniform so she can look for her sister. He tells her that he knows of a place where they may be keeping the children and leads her there. They are attacked in an alley by a gang outside, but Pen's mother comes and the gang runs off scared because she is one of the guards in the aerie and has a cattle prod like taser. Pen's mother then joins her in the hunt for Paige.
They go into a room that has big test tube like things where angels with scorpion tails are in the tanks feeding on humans. When Pen hears voices coming she hides and sees across the room a bunch of kids who look like they have been cut in various parts of their bodies and then sewn back together(she thinks they are all dead). She finds Paige there and she is still alive, but now has metal teeth extensions sharpened to razors (and can walk!) and Pen realizes these kids are the things they've been calling low demons, because when an angel sees Pen it attacks her but Paige attacks it and chews it up.
Raffe suddenly bursts into the room while bombs are going off overhead (the resistance is attacking the aerie) with the Hell angel and the Politician behind him. Apparently Raffe's wings have been sewn onto the Hell angel to make it seem like he is now an accepted angel and his batlike wings have been sewn onto Raffe to make it seem like he's truly fallen. Hell angel is attacking Raffe but Pen takes his sword (which has now rejected him and is so heavy he can't lift it) and attacks Hell angel. He smacks her aside and one of the scorpion angels stings her, paralyzing her.
Raffe comes to her, thinking she is dead since she's paralyzed, and she realizes he really does care for her because he is so upset over her death. The Hell angel and Politician leave because the Politician convinces it is better for the other angels to see Raffe as fallen rather than a martyr if they kill him.
Raffe takes Pen outside to where Obi, her mother, and Paige are and lays her down so they can take her. Pen doesn't see where he goes because she can't move even her eyes. Paige picks Pen up with superhuman strength for someone of her size and puts Pen in the truck along with the rest of the resistance.
The aerie collapses and everyone is very happy because they have made the first strike against the angels to let them know they are fighting back.
The book ends with Pen regaining feeling and she looks up to see that Raffe is flying above the truck.