The Ghost Orchid by Jonathon Kellerman

 Ghost Orchid is the latest Alex Delaware/Milo Sturgis novel. Milo is called to a murder scene. A man named Gio and a woman named Meigan are found dead, shot. It turns out she was married to someone else, but her husband had no clue she was fooling around, so Milo doesn't think he did it. So they wonder if Gio was the intended victim. With a little bit of luck and a lot of hard work they eventually figure out that Meigan was the intended victim--and figure out why. As always, a compelling tale from Jonathon Kellerman.