Jean Guy battles addiction - and is being used by the Chief Superintendent of the Surete.
Gamache is "disgraced" after he stopped a plot to  destruct a hyrdo-electric dam that would have destroyed lives and lands - but also cost the lives of some officers. 
Gamache's department is being dismantled and new adjuncts are disrespectful. 

Myrna's friend - last surviving sister of a famous set of quints - is murdered. While investigating - Gamache discovers the intrigue of the parents of the quints - and - corruption that runs from the Chief Superintendent up to the Prime Minister. Corruption that involves millions of dollars being diverted from infrastructure into people's personal pockets. 
Jean Guy is going to be the lure to bring Gamache to a location where both will die. But - the corrupt Chief Superintendent underestimates the people of Three Pines. 
We end with Jean Guy marrying Annie.