Irene Morrison, portrayed by Vera Farmiga, is a hardworking mother living in Upstate New York, struggling to raise her two boys while battling a cocaine addiction. As her eldest son, Ben (Jasper Daniels), eagerly anticipates his birthday, he asks her to buy a snake, leading Irene to suggest Lego instead. On Halloween night, Irene takes her children trick-or-treating, where she encounters Bob, a compassionate nurse played by Hugh Dillon.
Upon returning home, her husband Steve (Clint Jordan) surprises her with a toilet, excitedly announcing plans to add a second bathroom. However, when he attempts to initiate an intimate moment, Irene feels anything but sexy, redirecting the conversation towards their home improvement plans. The following day, in desperate need of a snake for Ben, Irene visits a reptile store but discovers she's short on cash. While her boys wait in the car, she sneaks off to see her dealer, who turns her down due to unpaid debts.
Struggling with the temptations at work, she considers the unthinkable: taking money from the cash register. After being denied by her dealer once again, she reluctantly checks herself into a drug rehabilitation center, where she meets Lucy (Caridad de la Luz), a fellow addict, and forms a supportive friendship. During her time there, she unexpectedly runs into Bob again, who encourages her and shares a book that aided him during his own recovery journey.
At her first Narcotics Anonymous meeting, Irene witnesses the triumphant celebration of a man's one-year sobriety, yet finds her resolve tested in the weeks that follow as she battles cravings while surrounded by friends using drugs casually. Unfortunately, her situation worsens when she's fired from her job after confessing her past substance abuse.
Lucy proposes an entrepreneurial venture, suggesting they start a cleaning business together, which Irene eagerly accepts. During a drive to her next NA meeting, she makes an impulsive decision that leads to an affair with Bob. As their relationship intensifies, he takes her to a snake breeder, allowing her to buy a snake for Ben as their intimacy blooms. However, that moment of bliss shatters when Irene catches Bob using heroin, resulting in an explosive confrontation that ends with her succumbing to drugs once again.
In a series of misguided attempts to find pleasure in toxic relationships, Irene and Steve try to reignite their spark through cocaine, but it quickly spirals out of control. Their chaos catches up with them when the police pull them over, resulting in their arrest for possessing drugs. With her future hanging in the balance, Irene consults a lawyer who outlines a demanding path to avoid a lengthy prison sentence. Faced with the consequences of her choices, Irene confesses her infidelity to Steve, who in anger tells her to leave.
Finding solace with Lucy, though their friendship strains due to her unreliability, Irene eventually finds a place to live and gains some custody of her children. After a Narcotics meeting, Bob unexpectedly appears to apologize, and despite the chaos, Irene decides to forgive him. However, as Bob's drug use spirals, Irene begins to suspect the dangers he poses to her children, leading her to confront him and make the difficult decision to ask him to leave for their well-being.
