When posting about a book or character, I'm often concerned that I'm treating common knowledge as though I've broken the Da Vinci Code. I've seen very little information about Maginnis so I don't believe that's the case here.
Maginnis first appeared in New Comics #4 in early 1936. His adventures continued until the 12th issue of the book, at which point it changed names to New Adventure Comics. New Comics was published by National Allied Publications, one of a number of companies that would eventually become DC Comics.
Maginnis' was tasked with travelling to "St. Pierre Country" for a little undercover work. Trappers were being assaulted and robbed and Maginnis was to investigate the matter and put an end to it.
I've tried to get my hands on copies of this book online but have not been successful to this point. However, the DC Comics Artists site provides a scan of the first page of the story which I've copied below.