Dead Ringer — Fredric Brown

“An engaging pair of detectives” at a traveling carnival look to capture a heartless killer in this entry in the Edgar Award�"winning series (The New York Times).
 
As a band of carnies moves through the Midwest putting on shows for the rubes, it seems a killer is traveling along with them. The first victim is one of the pint-size performers, and two more tragedies soon follow.
 
Fortunately, Ed Hunter and his uncle Ambrose are there -- and they have some sleuthing experience in their recent past. So even though Ed's a little distracted by a fetching female, they intend to track down this midway murderer . . .