X is the most recent title in the Kinsey Millhone series by Sue Grafton, at least until
Y Is for Yesterday comes out (per
SYKM) in August. It has dropped to $1.99 at Kindle and Kobo US.
Kindle US:
https://www.amazon.com/X-Kinsey-Mill...dp/B00TY3ZKJA/
Kobo US:
https://www.kobo.com/us/en/ebook/x-is-for