The Beekeeper’s Apprentice, which is the first in Laurie R King’s excellent (IMO) Mary Russell and Sherlock Holmes series, is free right now at Kindle UK, but not at Kobo UK or in the US. (Appears to be an issue of different publishers…)
Great book, great series…
You can see my review of the next-to-most-recent book in the series here.
Free for now at Kindle UK