Clues, Cash, Pieces of Murder - D B Elrogg - Bog

Why would someone buy seven ugly, winter hats in May? Police Consultant Milo Rathkey wanted to know but the buyer told him to mind his own business. Milo would have forgotten all about it if the Hat Man hadn't been found floating face down in a nearby river. Who murdered Hat Man? The clues center around a radio station contest that has treasure hunters pouring into Duluth in search of a quick payday. All Milo really wanted was four double-A batteries.