In 1910, New York socialite Olivia Stewart resists an arranged, socially advantageous marriage, and the mysterious death of her sister Eleanor in Northern California is an unhappy but convenient excuse to go West to investigate. On the way, she is thrown off a Bay area ship and nearly drowned, so she has a number of reasons to hide her identity when she arrives in Mercy Falls, Calif. Her shipboard rescuer turns out to be her dead sister's fiancé Harrison Bennett, about whom she has suspicions. Harrison in turn has his reasons to distrust the Stewart family. In this atmosphere of deceit and suspicion, attraction between Olivia and Harrison grows. Coble spins a tangled web in this third book in the Mercy Falls series (after The Lightkeeper's Bride), with red herrings and oodles of duplicity. Some complications (letters conveniently found) simply strain credibility, as does the revelation of the villain. Coble's fans won't mind that the plotting is a little loosely woven. (Apr.)