The Cat Who Had 60 Whiskers is the 29th (if you believe the blurb, and I'm certainly not going to count at
SYKM 
) and last in the Qwilleran/Koko/Yum Yum series by Lilian Jackson Braun. It has dropped to $1.99 at Kindle and Kobo US.
Kindle US:
https://www.amazon.com/Cat-Who-Had-W...dp/B000O76NJ6/
Kobo US:
https://www.kobo.com/us/en/ebook/the...-60-whiskers-1