In the Beginning - Nic Ward

Nic Ward wasn't always Hell's most infamous fallen angel. This is how his story began. In Higher Justice, a guardian angel by the name of Nicariel makes a deal with a demon to bring a killer to justice. In The Dizzy Fall, an Inquisitor is called in to investigate the murder of an angel. And in Devil's Crossroads, Lucifer's quiet life in the suburbs is upended by impossible news: God is dead. These three short stories take place before the start of the Nic Ward urban fantasy series.
You can start here or with the first full-length novel, Nothing Sacred.