Forbidden Angel by Tamar Sloan

An old enemy has risen. The thirst for the obsidian never died.
She’s the seventh daughter of an archangel. He’s a demon wanted by the Kings of Hell. Despite it all, they’ve fallen in love. Yet Gabby and Colt can’t escape who they are.
Even with secrets in Heaven and ancient enemies in Hell waiting for them, they’re going to have to face their differences. All so they can find the legendary spear with the power to end it all.
To do that, the spear’s three shards must be located. The search will take them to a mysterious island with new beings long thought to be extinct. Have they just discovered a new ally? Or another enemy…