Nine Coaches Waiting by the incomparable Mary Stewart has dropped to 99¢ at Amazon and Kobo and presumably elsewhere.
https://smile.amazon.com/gp/product/B00GW4OZH2/
https://www.kobo.com/us/en/ebook/nine-coaches-waiting-1
This was one of my top three Stewarts when I read them as a girl (the other two were
The Ivy Tree and
Wildfire at Midnight); I’m not entirely sure I’ll reread, but I can’t resist having it for a buck.
Crosspost in Mystery.