Black dog

"Ava has spent the last hundred years as a hellhound, the indentured servant of a reaper who tracks down errant souls and sends them to Hell. When a human necromancer convinces her to steal her reaper's Scythe, Ava lands in hot water with the demon Lilith, her reaper's boss. Lilith orders Ava to track down the last soul in her reaper's ledger, or die trying. But when Ava discovers that Lilith actually sent her after the fallen angel Azrael, she realizes she's being used as a pawn in Lilith's scheme to usurp the throne of Hell. Ava's had enough - after a hundred years of being used and enslaved, it's time for some payback. And Hell's never seen a fury like hers."--