Murder in Abbot’s Folly is the eighth in the Marsh and Daughter series by Amy Myers. It’s free right now at Kindle US and UK.
Free at Kindle US | Kindle UK
And, if you prefer to start with the first book in the series, The Wickenham Murders seems to be semi-permanently at $0.99/£0.99, with occasional dips below that.
Buy at Kindle US | Kindle UK