Plot it Yourself is the 32nd in the Nero Wolfe/Archie Goodwin series by Rex Stout. It has dropped to $1.99 at Kindle US as part of today's Daily Deal, matched at Kobo US. Grab it if you want it - Stout/Wolfe titles don't go on sale very often.
Kindle US:
https://www.amazon.com/PLOT-YOURSELF...dp/B004SOQ11G/
Kobo US:
https://www.kobo.com/us/en/ebook/plot-it-yourself