One of two current films dealing with the familial fallout of a teenager’s school shooting spree (Lynne Ramsay’s similarly themed We Need to Talk About Kevin debuted to mixed reviews at Cannes), Beautiful Boy has an intense insularity that is its biggest strength and major weakness. The story is elemental: Bill and Kate Carroll (Michael Sheen and Maria Bello), an unhappily married couple contemplating divorce, get a cosmic faceful of their failings after their college-freshman son, Sam (Kyle Gallner), kills several classmates and himself. They avoid reporters at the home of Kate’s brother and sister-in-law (Alan Tudyk and Moon Bloodgood), then at a motel, where they briefly rekindle their affection. Beautiful Boy is best in its early, pensive scenes, and its two leads are effective (particularly Bello), if implausibly detached. For his part, director/co-writer Shawn Ku astutely captures how the burden of guilt and avoidance passes back and forth between the Carrolls during their ordeal. But focusing so closely on this relationship finally underscores its artifice; even a sputtering marriage brims with acute details, and this one reveals only broad, actorly strokes. While Beautiful Boy is potent, even admirable (setting aside the question of why there are no scenes of the victims’ parents’ grief), it ultimately mistakes prim emotional monotony for gravity.