I don't consider it a spoiler, because it is evident right from the beginning of the story if not from the title itself, but I'm putting it under the SPOILER tag anyway: Obviously (or not), Alex, the main protagonist, doesn't believe in angels, heaven, etc. and when she starts seeing wings, she fears she is going insane, especially due to her family history. END OF SPOILER
However, the very same thing is also one of the strongest points of Sins of the Angels, because such an attitude is rather more realistic than most books of the genre adopt, which is a quick and more or less easy acceptance.
Anyway, that piece of knowledge the readers have but that Alex keeps trying to remain in denial about for nearly 70% of the story was frustrating as hell for me; I could only bear to read a few chapters at a time.
And after that point, when Alex catches up with the facts, I finished the rest in one go, because Sins of the Angels is ultimately a compelling, well-written story that adds the previously explored concepts their own unique twists.
Therefore, I am, now that we got that discrepancy between the characters' and the readers' knowledge, definitely interested to see where the rest of the series takes us.