The Cup of Morning Shadows (Twelve Treasures) by Rosemary Edghill

When librarian Ruth Marlowe discovers a Wild Gate to Elphame in her library's basement, she can't help but seize the opportunity to find her lost love, Rohannan Melior, High Lord of the House of the Silver Silences. But the journey will not prove easy, for Elphame is on the verge of revolution, and when Ruth learns who's behind it, she knows there is no turning back.