Pray for Scars by K.V. Rose

They say that Lucifer was a fallen angel, cast out from a heaven too pure for his brand of evil.
But they were wrong.
Lucifer was a god, biding his time until he found his own kingdom in hell.
When Sid Rain gets on the wrong side of the Unsaints, she finds out just how deep their ties run, and just how dark their sins are.
She finds out, too, that Lucifer is not at all who she thought he was.
He’s worse.
While she searches through the history of Alexandria and the twisted connection to her brother, she discovers not all secrets are meant to be shared, and sometimes running away is far less brutal than fighting back.