Lonelyheart 4122 is the fourth in the Inspector Purbright/Flaxborough series by Colin Watson. It has dropped to £0.99 at Kindle UK.
Buy at Kindle UK
I also note two other titles in this series are semi-long-term at $0.99/£0.99 in the US/UK – the first, which is always kind of nice if you want to try the series out, and the last, which is good, I guess, if you make it all the way through ?!