The first two titles in the Lord Edward Corinth & Verity Browne series by David Roberts have dropped to £0.99 each at Kindle UK. (Taken together with the Saylor title, I wonder if this is the start of another C&R Crime sale of first and/or second titles, similar to what we had a few months ago...)
Sweet Poison, #1:
https://www.amazon.co.uk/dp/B005E87YT8
Bones of the Buried, #2:
https://www.amazon.co.uk/dp/B005E8745W
And, similar to what @murraypaul points out for the Saylor series, there is also an omnibus for the first four titles in this series. And since the third and fourth titles are £3.99 each, if you know or suspect you will want all four, the omnibus at £6.99 is a better value:
https://www.amazon.co.uk/dp/B00GHK71MW
I read several of the early titles in this series in DTB, picked up on business trips to the UK, and enjoyed them, but the later titles have mostly stayed a smidge too expensive in e-book for me to indulge.