Rook

In the Sunken City that was once Paris the guillotine rules again, while Sophia Bellamy from the Commonwealth across the Channel Sea tries to rescue as many of the revolution's victims as she can smuggle out, and some prisoners disappear from their cells, with a red-tipped rook feather left in their place--but who is the mysterious Red Rook and where does Sophia's wealthy fiancé, René Hasard, fit in?