Struggling drug addict Olivia (Tea Falco) stumbles upon the hiding place of her younger half-brother, Lorenzo (Jacopo Olmo Antinori), in “Me and You.” (Severine Brigeot)

“Me and You” opens with a counseling session in which sullen 14-year-old Lorenzo Cuni (Jacopo Olmo Antinori) seems to answer every question that his therapist puts to him with the same shrugged-off rationalization: His misbehavior, his resentment — everything he does or feels — is completely “normal.”

“Can you explain what ‘normal’ means to you?” asks his doctor (Pippo Delbono), with a tone halfway between professional concern and amusement.

It’s a good question. Even by the standards of teenage rebellion, the protagonist of Bernardo Bertolucci’s engaging tale of awkward adolescence is a bit of a weirdo, not to mention a recidivist one. A mere 20 minutes into the film, Lorenzo has, apparently not for the first time, run away from home.

He doesn’t go far this time. Instead of traveling out of town with his class for a school trip, Lorenzo uses the cash for it to buy a week’s worth of junk food, setting up a cozy if somewhat claustrophobic encampment in a basement storage unit of the apartment building that he lives in with his divorced mother (Sonia Bergamasco). When she calls her son on his cellphone the next day to check up on him, Lorenzo regales Mom with tales of how much fun he’s having, even though he’s only a few floors away from her, listening to MP3s and eating Nutella sandwiches on a ratty mattress.

His only other entertainment in this subterranean retreat is, appropriately enough, a copy of the novel “The Vampire Lestat” and a recently purchased ant farm.

All that changes with the arrival of Olivia (Tea Falco), Lorenzo’s 25-year-old half-sister by Lorenzo’s father (who, although he never appears in the film, seems to have at least a couple of ex-wives). Looking for a place to crash while she kicks a heroin habit, the foul-mouthed Olivia tumbles onto Lorenzo’s lair quite accidentally, though she quickly leverages the situation, forcing her brother to take her in lest she expose his hideout.

Their relationship — brief but intense — unfolds with surprising tenderness in this adaptation of Niccolo Ammaniti’s 2010 novel. Olivia’s detox is a painful one, and Lorenzo must help her through it, calling upon previously unrecognized reservoirs of compassion. At the same time, the film is unsentimental. Though the setting is a retreat from the world, where not terribly much happens, within its confines Lorenzo gets an eye-opener about both human frailty and interconnectedness, courtesy of someone even more troubled than he is.

Ironically, it’s Olivia’s effort to withdraw — not just from drugs, but from her past — that compels Lorenzo to engage with the present in a way that he hasn’t previously been capable of, or willing to attempt. Prone to shutting himself off from commitment with headphones, hoodies or his own hostility, Lorenzo discovers a bond with his half-sister that’s both empowering and healing.

“Me and You” isn’t exactly a coming-of-age story. By the end of his week with Olivia, it’s clear that our hero still has a lot of growing up to do. But over the course of a few short days underground, one other thing becomes clear. By trying to live off the grid, Lorenzo discovers how inextricably tethered to each other we all are.

★ ★ ★

Unrated. At the West End Cinema. Contains coarse language, drug content, brief nudity and underage drinking. In Italian with subtitles.
96 minutes.