Ranger McIntyre: Unmentionable Murders - A Ranger McIntyre Mystery, #1

In 1920, Rocky Mountain National Park is only five years old. With the Great War finally over and the automobile readily available, many Americans are motoring to the National Parks for vacation. Ranger McIntyre's main job is to protect the wilderness from the campers and sightseers. But a body, clad only in underpants, is discovered floating beneath a waterfall. Shortly thereafter a second corpse, also clothed only in underwear, is found lying on a log beside a remote lake.
Ranger McIntyre's usual duties as a park ranger do not include murder-or people in their underwear, for that matter-but he starts putting pieces of the puzzle together until they lead him to a backcountry hut and a photographer who orders him to disrobe-at gunpoint. Ranger McIntyre is drawn into an FBI investigation involving a suspect who is selling salacious photographs of nudes who appear to be very, very dead.
McIntyre's interaction with the FBI agent is made even more embarrassing by the fact that the agent's secretary is the drop-dead gorgeous Violet Coteau, who looks like a flapper. and acts like an agent.