Disappointing opus

Like others I waited impatiently for this album Fred Vargas, and as others I was disappointed by this latest survey Adamsberg. The historical background is, as always, but the characters appear as absent, plated dialogues (even those between Adamsberg and Danglard, as if a "made" of Adamsberg and one from Danglard). The contrast is even more stark The Furious Force, one of the best in the series.
If I remove the disappointment in contrast to other Fred Vargas I would probably put 3 stars because it's still "not bad", but not quite up to Fred Vargas ...