No Mark upon Her is the fourteenth in the Duncan Kincaid/Gemma James series by Deborah Crombie. It has dropped to $1.99 at Kindle and Kobo US.
Kindle US: https://www.amazon.com/dp/B005HFI8YS
Kobo US: https://www.kobo.com/us/en/ebook/no-mark-upon-her