The Hanged Man of Saint-Pholien is the third book in the Inspector Maigret series, although mislabeled #4 at both Audible and Amazon. I accidentally read it before the second book (which is labeled #3).
Maigret is on a trip for his work when he notices a man mailing large bundles of money. Because he is curious, Maigret follows the man, assuming that he is a crook of some sort. Eventually the man commits suicide and Maigret has to solve the case, both to find out what has happened and to see if Maigret’s own involvement was the cause of the suicide.
This is not a murder mystery as much as a psychological book exploring the way that guilt drives our actions. This is exactly what I like about mysteries, the exploration of the characters and their motivations more than the ‘who dune it’. This is quick enough to read in a couple days without much problem.
The Kindle Edition is on sale for $2.99 as I am writing this and the audiobook is $3.49 with purchase of the Kindle Edition.