Ravishing in Red by Madeline Hunter

The first novel in a magnificent new quartet of historical romance
Audrianna Kelmsleigh is unattached, independent-and armed. Her adversary is Lord Sebastian Sommerhays. What they have in common is Audrianna's father, who died in a scandalous conspiracy-a deserved death in Sebastian's eyes. Audrianna vows to clear her father's name, never expecting to fall in love with the man devoted to destroying it...