The Dunraven Hoard Murders — James C. Work

With a two-week vacation so close he can feel it, Rocky Mountain National Park Ranger Tim McIntyre is torn away from fantasies about how much fly-fishing he can fit in when he's roped into using his free time for an informal investigation as a favor to a friend. That's fine with McIntyre, because the friend is FBI secretary Vi Coteau, and investigating at his sweetheart's behest makes it likely that he'll be spending time in close quarters with her. And no quarters could be closer than exploring Colorado's labyrinthine mines, where upper-crust undergraduate Richard Leup and two of his fraternity brothers have been exploring in search of that well-known buried treasure, the Dunraven Hoard. One of the boys has died during the explorations, and the other two are the most likely suspects if the death turns out to be murder and not misadventure...