Her Shadow (Four Winds #3, Harlequin Intrigue #457)

Lucas Blackhorse, with eye like midnight and a smile like a summer day, is a doctor - a healer of bodies, a knower of hearts. But luckily for Marlee Smith, the last bachelor Blackhorse brother doesn't know what she's kept hidden. For which is a darker, deeper secret - Marlee's past or her love for Lucas? But with a mysterious illness sweeping Four Winds, and once-close friendships now charged with suspicion and fear, fingers point to Marlee and whispers frame her. Suddenly the past she's run from is a very present threat. Her only hope is the love she'd concealed - and Lucas.