Midnight Enchantment (Dark Magick, #4)

 A quest for freedom may be derailed by their intense attraction...
Niall Quinn, mage and the finest thief in the Black Tower, is the fae's best hope for freedom. Only he stands a chance of tracking down and retrieving the missing bosca fadbh pieces from the Summer Queen. But he meets his match in Elizabeth Cely Saintjohn, who has taken control of the pieces on the Summer Queen's behalf—and has refused to give them up.
Elizabeth is an asrai, a rare English water fae, and she may be the only one in Piefferburg stealthier than Niall. She has her own reasons for guarding the two pieces and wanting the walls of Piefferburg to remain intact—even if it means denying her fae sisters and brothers their freedom. Her mother's life depends on it.
Torn between his duty to obtain the pieces at any cost—and the shocking lust Elizabeth has stirred in him—Niall must convince Elizabeth to surrender the pieces, or else he may have no choice but to destroy her and all she holds dear.