Ashes of Eden by Mandi Konesni

After being tainted by Leviathan blood, an Archangel must collect angelic relics and return them to Heaven before the transit of Mercury to prevent the Undoing… a period where demons can take control of the earth and negate the power of Heaven.
To earn back his wings, he’s tasked with preventing this from occurring by any means necessary. Even if it includes working with a Cambion female who is too nosy for her own good, or getting caught breaking into the Vatican. They did say ‘any means necessary’, didn’t they?
Evil is insidious, and lurks in the most unassuming of disguises. But people are stronger together, and true love is worth fighting for, even if you have to give up everything you thought you needed and wanted in order to keep it. He may be a protector of the world, but he failed to protect something far more important- his heart.
Sometimes, redemption comes in a way you least expect it to. Sometimes, sacrifice is worth the cost.