What's unexpected as well as moving about this film by Olivier Assayas, at least in relation to his other recent features (Cold Water, Irma Vep), is how sweet tempered most of it is. Split into six chapters, with several weeks or months separating one section and the next, it follows a group of close friends--mainly a novelist who's just turned 40 (Francois Cluzet) and is becoming ill, a writer-editor in his 30s (Mathieu Amalric), and their current and former lovers (Virginie Ledoyen, Jeanne Balibar, Arsinee Khanjian, and Mia Hansen-Love). What we don't know about these characters--and what we don't see in certain scenes--is often as interesting and as important as what we know and see, and Assayas's sense of how relationships evolve between people over time is conveyed with a rich and vivid novelistic density. With Nathalie Richard and Alex Descas. Music Box, Friday through Thursday, September 17 through 23.