Horn Gate

HORN GATE: Open at your own risk.
Librarian Isaac Stein spends his lumpy, lonely days restoring forgotten books, until the night he steals an invitation to a scandalous club steeped in sin. Descending into its bowels, he accidentally discovers Scratch, a wounded demon who feeds on lust.
Consorting with a mortal is a bad idea, but Scratch can't resist the man who knows how to open the portal that will free him and his kind. After centuries of possessing mortals, he finds himself longing to surrender.
To be together, Isaac and Scratch must flirt with damnation and escape an inhuman trafficking ring—and they have to open their hearts or they will never unlock the Horn Gate.