Black angels

For Alex Herondale too much angelic blood eats away at his mortality. He doesn't sleep well with nightmares from the past and future mending into the life slowly eating at him.
Much like his father he had a bitterness that seemed to finally be pulled away with a mysterious girl.
But she's dying from a curse like ice in her blood. Not to mention an infernal device left as a contingency plan by Sebastian is in someone's hands. All of it is a puzzle of repeating events that could bring an end to all that is good.