The Wickenham Murders is the first in the Marsh & Daughter series by Amy Myers. It is free right now at Kindle US and UK. There is also an omnibus of Marsh & Daughter titles that contained this one that has been on sale in the past, so normally I'd say to check carefully, but free is free, so...
Kindle US:
https://www.amazon.com/Wickenham-Mur...dp/B07CJ7WDLT/
Kindle UK:
https://www.amazon.co.uk/Wickenham-M...dp/B07CJ7WDLT/