Knight's Prize by Sarah McKerrigan
Miriel is the younger sister of the infamous Warrior Maids of Rivenloch, Dierdre and Helena, who were raised by their father to wield swords and defend their lands. Miriel was her mother's daughter, and was raised to be meek and shy. But at night, when the people of Castle Rivenloch are sleeping, Miriel dresses in black and takes to the forest, where her true nature comes out. Having been trained in martial arts and having collected unique weapons from the Far East for years, Miriel's alter-ego is known to the people of Rivenloch as The Shadow. The Shadow is a known thief, though nobody can catch him. And Miriel likes it that way.But the Shadow's exploits are soon to catch up with Miriel. Sir Rand le Brun is hired by a local Scottish lord to catch the Shadow, and to do so, he has come to the Castle Rivenloch with a cover story. He pretends to be courting the youngest Rivenloch sister , Miriel, the very person he seeks to catch! Soon the two are engaged in a tangle of courtship by day and a battle to the death by night. And though they're falling in love with each other, Miriel's secret identity could destroy everything.