Directed by Griffin Dunne — who, as the son of jet-setting Vanity Fair columnist Dominick Dunne, knows a thing or two about rubbing elbows with the wealthy — the 1980-set Fierce People is chiefly about the collision of classes, and how even affluent factions result to primitive behavior. A collection of wildly colorful characters in search of some sort of narrative cohesiveness, though, the movie — adapted by screenwriter Dirk Wittenborn from his own novel — never gels into something more than the occasional, piecemeal entertainment of its fractured parts.

Anton Yelchin (above right) stars as 15-year-old Finn, a well-intentioned kid pinched buying drugs for his junkie masseuse mother, Liz (Diane Lane). This bust wrecks Finn’s plans of spending the summer with his estranged anthropologist father, studying the remote jungle Ishkanani tribe. Instead, Liz drags Finn out to the rural New Jersey enclave of Vlyvalle, to spend the summer with her eccentric sugar daddy, Ogden Osborne (Donald Sutherland). While Liz begins attending AA meetings and strikes up a dubious relationship with Osborne’s physician (Christopher Shyer), observant, hoi polloi gate-crasher Finn, meanwhile, settles into life with the “tribe” of wealthy country-clubbers that inhabit his new home.

He finds a brazen flirt in maid Jilly (Paz de la Huerta), a kinda-sorta girlfriend in Osborne’s granddaughter, Maya (Kristen Stewart), and a strange mentor and advocate in Maya’s older brother Bryce (Chris Evans, above left), a rakish college washout. Unfortunately, just as Finn thinks he’s found his way, things begin to spiral out of control. Sexual awakenings both pleasant and quite rude then ensue, and Finn begins to see that wealth can be a mask for some nasty deeds.

Yes, one might be surprised to learn that Fierce People, in its third act, essentially becomes a whodunit about Finn’s ass-rape at the hands of a mysterious assailant. Or perhaps that’s not a surprise. After all, that seems to make about as much sense as some of the arbitrariness on display here. It’s not necessarily the consistent collision of wackiness and earnest symbolism that hamstrings Fierce People. After all, a film need only unfold in a world that makes sense within the parameters of its own devising. But the tucked away cul-de-sac of exclusivity in which Fierce People unfolds never quite feels fully sketched out. The end result feels like a grouping of potentially interesting, if sometimes thinly drawn, characters in service of an undercooked narrative premise we see reflected more starkly every day in tabloid celebrity misbehavior. It’s just too contrived to be taken seriously, and too burdened with sometimes thought-provoking parallel imagery to be enjoyed as a trashy, turn-off-your-brain delight. (After Dark Films, R, 107 minutes)