The path from starring in a Michael Bay explodapalooza to winning a Special Jury Award at Sundance is certainly the road less traveled. As a poverty-stricken Dubliner who cares for his alcoholic mother in Glassland, Jack Reynor does just that. After a turn in Transformers: Age of Extinction, Reynor plays John, a young man thrust into a caretaker role for his soggy mother (Toni Collette), whom we first encounter next to a pile of vomit on her pillow. When he’s not rushing his mom to the E.R., throwing out her regenerating stashes of booze or trying to coax her into rehab, John works the graveyard shift as a Dublin cabbie, which seems to also involve some mysterious transporter work for the sex trade.

Money is scarce. John mixes in water to stretch the last drops of milk for his cereal. A trip to the grocery store yields only some root vegetables. Amidst the misery of babysitting his drunken mother, John carves out a sliver of joy by visiting his brother Kit (Harry Nagle), who has Down syndrome, and blowing off steam with foul-mouthed pal Shane (Will Poulter). But his life’s goal remains finding a way to get his mother the help she needs, to revive the woman who smiles and dances but who has devolved into sodden and volatile mess.

The sophomore effort of director Gerard Barrett, Glassland could easily wallow in its squalor and heartbreak. Yet there are transcendent moments amid the sorrow. One night, John allows himself to take a break from policing his mother’s self-destruction, and the two enjoy glasses of wine and listen to music together. She opens up and reveals unsavory details from her past and rationalizes her open hostility toward her disabled son. And John truly loves his brother, leading the singing at Kit’s 18th birthday party and giving him a counterfeit birthday card from their mother.

Barrett creates a claustrophobic atmosphere throughout Glassland, framing many of his shots with corridors, walls or shadows restricting the view. He keeps the camera close to his subjects, but we’re not always given a clear look. As John’s soft touch breaks down and he rages at his mother—who is having second thoughts about checking into rehab—about her alcoholism breaking his heart every single day, we view much of this from the backseat of a car. Largely relying on natural light and bereft of music (with the notable exception of “Tainted Love” in one scene), the film is stark and beautiful despite its downbeat subject matter.

Glassland’s modest ambitions don’t excuse it from some missteps, however. Despite carrying herself as appropriately haggard and forlorn, Collette isn’t particularly well-cast for the mother role and her most emotive moments (including a feral outburst when she discovers her booze stash missing) feel slightly strained. The human trafficking subplot also drags the film down—it’s so ambiguously handled that its role in the film’s conclusion will leave more viewers scratching their heads than stroking their chins. But this is ultimately Reynor’s show, and he gives a powerful performance in his return to arty drama (after his 2012 breakthrough in Lenny Abrahamson’s What Richard Did), proving his foray into CGI action films wasn’t a permanent lane change. As a slow-burning, micro-budgeted Irish indie steeped in grim realities and propulsive emotions, Glassland is a vehicle that allows Reynor to truly shine.