Not one of the best ones by a long shot. The story meandered, felt disjointed - something that was not helped by the secondary plot introduction - and the killer was telegraphed from the first scene they were in.
Normally, I love this series and I love these characters, but between the meandering and the lack of mystery behind a string of murders, there wasn't much to keep me engaged. The author also seemed more melancholy and wistful than usual, with less of the humour I enjoy so much.
All together, it resulted in a poor showing for book #21. Hopefully #22 regains the series stride.