Proof, by Dick Francis, has dropped to $1.99 at Kindle and Kobo US. Although I've read and enjoyed most of Francis' books, this one (in my mind) rose slightly above some of the others, since I had never heard of "wine forgery" before...
Kindle US:
https://www.amazon.com/Proof-Dick-Fr...dp/B00452V486/
Kobo US:
https://www.kobo.com/us/en/ebook/proof-2
Strangely enough, I had just referred to
Proof yesterday in the non-fiction thread, because one of the Amazon US Daily Deal titles yesterday was about a non-fictional wine forger, and I mentioned
Proof as my first exposure to the concept.
In Vino Duplicitas had dropped to $2.99 as part of yesterday's sale, but is still at $2.99 as of this morning, at Kindle US only, not Kobo. Link if you're interested in that too:
https://www.amazon.com/Vino-Duplicit...dp/B01M6WQEP9/