I finished Martin Edwards' The Serpent Pool last night and I really enjoyed it. I loved the way all the links were revealed between the various characters and the denouement. I can't really say too much about the plot without revealing all - suffice it to say the mystery is complex and satisfying. The development of the characters - DCI Hannah Scarlett - her partner, rare book dealer Marc Amos - and historian Daniel Kind - is interesting. All three are rounded characters with faults as well as good points. As ever in this series the Lake District plays a big part in the story and broods over all.
I read it over three evenings and found it compelling reading. I liked how all the clues built up but I still didn't work out completely who was responsible before the end. I liked the background - Thomas De Quincey, rare books and printing. I recommend it. I have posted a review on Amazon which last time I checked hasn't yet appeared.