Something More Than Night, by Ian Tregillis.

The premise: set on an earth of the indetermine near future, the archangel Gabriel has just been been murdered, and heaven is aswirl with rumour. A fallen angel, Bayliss, sets off on a noir, detectivive-style hunt to figure out the mystery behind it. But first he has to enlist Gabriel’s replacement, and accidentally christens an abruptly deceased young woman, Molly, to take the archangels vacant place in the pantheon. Then things get really interesting.

A wonderful story. Loved it from start to finish, and would heartily recommend it to anyone interested in supernatural intrigue, angels, demons, or fantasy/sci-fi noir.