Three titles in Edward Marston's Railway Detective series are on sale at Kindle UK right now, two old, and one most-recent-in-series (and holiday themed).
The Railway Viaduct, #3, £0.99
Kindle UK:
https://www.amazon.co.uk/dp/B006WB7MXO
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B006WB7MXO
The Iron Horse, #4, £0.99
Kindle UK:
https://www.amazon.co.uk/dp/B006WB7ONM
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B006WB7ONM
The Railway Detective's Christmas Case, #20 (and most recent, until a new one comes out next April), £2.79
Kindle UK:
https://www.amazon.co.uk/dp/B09SXHY1R1
Kindle UK/Smile:
https://smile.amazon.co.uk/dp/B09SXHY1R1