Professor John Stubbs. Originally published in 1945, this re-formatting and re-release came out 16th Jan 2019 from Dover. It's 144 pages and this edition is available in paperback and ebook formats.
This is a classic golden age British mystery. R.T. Campbell was the pseudonym of poet and author Ruthven Todd. As a bio-engineer, I really enjoyed reading the 1940s genetics (the murder takes place at a professional conference of geneticists). The book has held up surprisingly well in my opinion. Some of the dialogue is a bit dated, but all in all, it's very well written, fast moving, well plotted and has a satisfying denouement.
It's a very fast read (I would call it a long novella or a very short novel). As in many (most?) murder mysteries of the time period, the corpse was a thoroughly unlikable jerk; no tears were shed. There is a smaller than normal pool of suspects and Stubbs has to resort to subterfuge to deliver the guilty party. All in all a nice read by a lesser known author from the golden age. While it's not up to Christie, Marsh, Carr, Tey, or Sayers, it's a completely readable and diverting mystery.
Disclosure: I received an ARC at no cost from the author/publisher for review purposes