Author is Anthony Boucher who was honored by using his name for the world mystery conference - Bouchercon.
Setting for this story is Hollywood, 1939.
From the cover:
When a Hollywood studio announces plans to film a Conan Doyle classic, it arouses the ire of a group of Sherlock Holmes aficionados. Soon all sorts of thrilling things begin to happen, such as murder with a disappearing corpse, cryptograms, a couple of cock-eyed adventures in the best Holmes tradition and all the odd trimmings, including a Watson who is a cop, not a doctor.
Boucher obviously had a grand time writing this outlandish whodunit, and you will have an equally fun time reading it if you let yourself be taken along for the ride.
Boucher wrote a few golden age mysteries and science fiction tales, but was more prolific as a reviewer and critic of other people's work. His reviews from his years with the San Francisco Chronicle have been compiled in two volumes by Francis M. Nevins and published by Ramble House in 2002. These are great volumes to peruse while looking for other golden age mysteries to read (and avoid.)
Having read thousands of other mysteries, Boucher was qualified to write some of his own. "Irregulars" has some of the elements of the typical golden age mystery: a house where murder occurs and all the suspects are gathered under one roof for the duration, an impossible crime, and a plucky heroine. It also has elements that I can't resist: charts showing suspects and alibis, a diagram of the house, graphic representations of the clues and solution. The only thing missing from the Carrol & Graf paperback edition I have is a crime map on the back cover.
If you are prepared to have your leg pulled for 250-odd pages, dig in.