Queen of the Deep — Kay Kenyon

On the streets of New York, Jane Gray meets an intriguing man who claims to be the impossible: an imaginary playmate from her childhood: Prince Starling. Determined to know the truth, Jane tracks him into another realm. This is the world of the Palazzo, a magical ship which is both a colossal steam vessel and a Renaissance kingdom. Ruling over its denizens--both human and otherwise--is an exotic and dangerous queen. Jane must find her way home, but the path is hopelessly lost. Promising romance, the enigmatic Prince Starling and big-hearted crime lord Niccolo vie for Jane's heart. But she has her eye on the pilot house. Who--or what--guides the Palazzo, and what is the urgent secret of its endless voyage? As a shocking destination looms into view, Jane must choose both a lover and a ship's course, one that may avoid the end of all things.