Blood by Moonlight

An Irishman enamored, is a dangerous thing. Above all when he consorts with the Gentle People.

Aengus loves Lady Agatha, but he is poor, and she is bedmate to a very wealthy man. Therefore Aengus kills the Sun and plunges the world into eternal Night, and a world where the wealthy man and all his ilk, sleep without end. And Aengus gains the body, if not the heart, of his ladylove.

And then Lady Agatha learns magic in her turn...