American audiences are still getting to know the great French actor Mathieu Amalric — you may remember him as the Euro Bond villain du jour in Quantum of Solace, paralyzed memoirist in The Diving Bell and the Butterfly, secretive butler in The Grand Budapest Hotel — and his latest project turns our not quite having a read on the guy into a distinct advantage. In The Blue Room, which he directed, Amalric plays a somewhat mysterious man whose adulterous affair has led to a police investigation. The story unfolds as a whodunit, but without right away revealing just what the “it” in question is. Amalric co-scripted and co-stars with his real-life partner Stephanie Cleau, sourcing their material from the late Belgian author Georges Simenon, a frequent movie adaptee and one-man factory of psychologically penetrating crime thrillers. Working through the puzzle of story fragments right along with the audience here are a bemused wife (Léa Drucker), a probing judge (Laurent Poitrenaux), and indeed also our alert yet hapless protagonist himself. As both actor and director, Amalric makes short work of this stuff, including the ever-welcome Vertigo homage; such is his restraint that the aura of the film seems nonchalant even as its emotional scope seems grandly tragic. (Relatedly, Gregoire Hetzel’s lushly effusive score plays well against cinematographer Christophe Beaucarne’s artful if aloof compositions.) Being a dark, swift take on sex, death, and judgment, The Blue Room hits the French-thriller sweet spot. Being an Amalric affair, it benefits, too, from a certain je ne sais quoi.