Filmmakers Mark and Jay Duplass and their superior cast have together created a memorable portrait of a very particular kind of familial dysfunction: the uncomfortably close relationship between a single mother and her grown son. In Cyrus, we watch this relationship go through a painful and trying transition through the eyes of an outsider - the mother's new boyfriend. With the ever-morphing interpersonal dynamics of these three characters as its sole concern, Cyrus succeeds both as an observational drama, a charming romance, and a teeth-grittingly funny comedy.

John (John C. Reilly) has been divorced for seven years from Jamie (Catherine Keener), who encourages her shy and lonely ex to get out and meet women. At a party one night, a very drunk John meets Molly (Marisa Tomei) and, seemingly against the odds, sparks fly immediately. Not long after their first few evenings together, John discovers that Molly has a grown son, Cyrus (Jonah Hill), still living at home. The first interactions of the three are chock full of awkwardness - factors here include Cyrus' age, the newness of John and Molly's relationship, Cyrus' over-dependence on Molly, and Molly's tendency to coddle her 21-year-old son. It soon becomes apparent that Cyrus has no qualms about manipulating Molly and her relationship with John, all in order to avoid taking responsibility for himself and facing life as an independent adult.

What is perhaps most remarkable about Cyrus is that it doesn't paint Molly and Cyrus' relationship as something that is merely creepy, or comical, or one-sided in any way. Both mother and son are culpable in the dysfunction at play here, even though Cyrus, whose behavior borders on the sociopathic, is certainly the focus of the conflict with John. Molly is slow to perceive Cyrus' manipulative machinations, but when she does, she also understands that she has enabled years of antisocial tendencies and we see her grappling with her own sense of responsibility.

This probably all sounds very heavy-duty, but what's so remarkable about the weight of the mother-son relationship is that it comes off as so authentic in the midst of truly funny scenes and skillfully balanced performances by Reilly and Hill. Reilly is the straight man here to Hill's Uncle Fester-inspired Cyrus. Their comic chemistry is fantastic, in moments both large and small - and particularly when John and Cyrus declare war on each other. Hill carefully modulates both insidious duplicity and youthful confusion, while Reilly's strength here is generating genuine "nice guy" vibes without overplaying a single line or gesture. As Molly, Tomei displays a loving obliviousness while Cyrus fucks with John early on in the story - but this turns into a credibly mature honesty when forced to confront her son about his actions.

The Duplass brothers have used a highly improvisational filmmaking style, not in order to allow these comic actors to find laughs, but to enable them to search for the real human drama beneath what is an otherwise comic situation. It's a highly collaborative technique, and all of the actors rise to the challenge beautifully. It's a brave, forthright approach to a character-based story that eschews visual flourishes of any kind. Working loose, with only a few actors and even fewer locations, the Duplasses bring off a film of impressive emotional depth that addresses a strange but wholly realistic situation. Summer comedies aren't typically known for providing audiences with true cinematic experiences, but Cyrus is an exception.

Casey Burchby lives in Northern California: Twitter, Tumblr.