Connecting Rooms by Jayne Ann Krentz

Amy Comfort is a real estate agent on Misplaced Island, a quaint, remote town located off the coast of Washington. When she sells an old Victorian manse to the sultry, sexy Owen Sweet, a private investigator relocating from Seattle, sparks fly from the get-go, though both Amy and Owen decidedly ignore their natural chemistry.
Until, that is, Amy enlists Owen’s help in looking into her aunt Bernice’s fiance Arthur Crabshaw, who Amy suspects is not what he seems. To keep their cover intact, Amy and Owen pretend to be a lovestruck, newly engaged couple, as they travel to Villantry, Washington, to investigate Arthur. When the mystery surrounding Arthur begins to spin out of control, Amy and Owen must trust in each other to stay alive. But, when the lines between their make-believe courtship and reality begin to blur, will the faux-couple end up with something aside from what they had set out to find?