Carlotta
The Castillian spy known as "El Chacal" has been operating inside Montaigne since not long after the start of the Montaigne-Castille war, and has been a thorn in the side of L'Empereur for as long as he - now revealed to be a she - has been known. El Chacal has disrupted troop movements, intercepted messengers, drugged water supplies and worse.
Our heroes encountered El Chacal when the spy was to meet with a traitorous colonel at an opera. There, they learned that he was a she: the talented dark-haired beauty Carlotta, a soprano of exquisite quality. She escaped the heroes through a clever ruse, but surely will cross paths with them again.