The Dark Horse is the fifth in Craig Johnson's Walt Longmire series. It has dropped to $1.99 in the US today.
Kindle US:
https://www.amazon.com/dp/B0026NBZCQ
Kindle US/Smile:
https://smile.amazon.com/dp/B0026NBZCQ
Kobo US:
https://www.kobo.com/us/en/ebook/the-dark-horse-2