The Onyx Court
What began as a single book has now morphed into a very loose series. Midnight Never Come, the Elizabethan first installment, is due out June 9th. Meanwhile, I will be spending my summer writing And Ashes Lie, a loosely connected sequel set during the Great Fire of London in 1666. After that, there may be more.
The unifying thread of the series is the Onyx Court: a hidden faerie kingdom existing beneath London itself. These are urban fantasy novels in the literal sense; they focus on a city, though they are not contemporary in their setting. For me, part of the great appeal of continuing on with the series is that I will build up London over time, weaving my own, secret history into the palimpsest that is the real modern and historical place. (There's a mixed metaphor for you.)
Plus, I get to make research trips to London as "business." ;-)