The "Big Book of the Continental Op" has an introduction at the start of this short story which was initially published in "Black Mask" magazine. That magazine said: "Here is a detective story which we think will please all comers. It is a happy combination of deduction and swift action." A doctor-surgeon with a good reputation committed suicide for no apparent reason. But questions arose and the Op was asked to get involved at the request of the doctor's widow. Librarian's note #1: this entry is for the story, "Zigzags of Treachery." Entries for collections of short stories, and each of the other individual stories, can be found elsewhere on Goodreads. There are a total of 28 short stories plus one incomplete; they can all be found by searching Goodreads for: "a Continental Op Short Story." Librarian's note #2: there are also two Continental Op novels, "Red Harvest" (also known as "The Cleansing of Poisonville), and "The Dain Curse."