A tense psychological thriller unfolds around a broken family and a distant sister-in-law who struggles to find a place with them. The film opens with Laura taking her children, Aiden and Mia, to visit their father, Richard, who soon reveals that he is engaged to Grace and plans to marry in the fall. The revelation fuels a bitter clash, and Laura storms out, returning home where she takes her own life. The family mourns, and Laura’s death casts a heavy shadow over Mia, who, as part of their devout Catholic background, believes Laura may not enter heaven for killing herself.
Six months pass, and Richard proposes a Christmas gathering at Grace’s family lodge in Massachusetts to help the kids connect with Grace. Aiden and Mia resist this plan, blaming Grace for Laura’s death. Aiden lashes out, calling Grace a “psycho.” On Richard’s computer, the siblings uncover troubling background details: Grace was once connected to a religious cult led by her father, where members supposedly sacrificed themselves so she could carry on the cult’s teachings. Images show cult members blindfolded, mouths taped with “SIN” written on them. Richard knows some of this, but he and Grace insist Grace has left that past behind and is trying to live a normal life.
The trip to the lodge brings Grace into closer, awkward proximity with Aiden and Mia, who remain distant and often cold. Grace makes earnest attempts to reach out, even as the kids can hear her and Richard together in a neighboring room. When they step outside for a stroll, Grace wears Laura’s hat, unsettling Mia and Aiden. The moment grows more tense when Mia’s doll falls into the freezing water; Grace fumbles to retrieve it but is pulled back by Richard. The ice gives way, and Grace is saved by Richard, who immediately heads back to work, leaving Grace in charge at the lodge for a stretch with the kids and Grady, Grace’s dog.
Richard’s absence grows longer as he works in the city, and Grace tries to nurture a bond with the children. Yet their suspicion and hostility persist. Grace confronts a boundary-crossing moment when Aiden appears to spy on her in the shower, at which point she calls him out for loitering in her privacy. Gradually, Mia begins to open up and even shares TV time with Grace, signaling a fragile shift in their relationship.
A sudden storm traps them inside the cabin, cutting power and leaving them snowed in. Basic necessities—medication, food, and even Grady—start to vanish. Grace suspects the kids of pranking her, but other oddities hint at something more insidious: clocks move forward by themselves, the word “REPENT” is scrawled on a mirror, and Grace feels increasingly watched. The line between reality and Grace’s perception blurs as she begins hearing the voice of her father preaching, and her sleep is disturbed by unsettling visions. With no medicine and dwindling warmth, Grace’s grip on sanity loosens, and Aiden shares a dream about a heater malfunction that would cause their deaths, suggesting they might all be dead.
Grace attempts to seek help in town but becomes lost, eventually stumbling upon a cross-shaped cabin before finding her way back to the lodge. There, she discovers a frame bearing a photo of Aiden and Mia with an “In Loving Memory” caption and a story claiming that they died from carbon monoxide poisoning on December 22nd. The siblings insist that Grace and the others are dead, while Aiden is convinced they are in purgatory. The night wears on as Grace becomes more unmoored, and Grady is found frozen to death, a tragedy that devastates Mia and deepens the rift with Grace.
With Grace certain that they are in purgatory, she endures the cold outdoors through the night, praying beside the snow and sacrificing herself to prove their sins can be repented. The children’ s plans to gaslight Grace become brutal in their own right: they steal her medications and other belongings, hide them in a crawlspace, and use a staged audio of Grace’s father’s sermons to torment her. They retreat to the attic as fear grips them all.
Dawn reveals Richard’s return to the lodge, where Grace lies frostbitten and unhinged. She has the kids in tow, and Richard’s gun is still within reach. Grace remains convinced that they are dead and, in a desperate bid to confirm it, shoots Richard in the head as he tries to calm her. The children rush to his body, then flee outside as Grace corners them. Their car is stuck in the snow, and Grace closes in, seizing control of the scene.
In the final tableau, Grace forces the kids to sit at the table with Richard’s corpse and compels them to sing a church hymn. She tapes their mouths with strips marked “SIN” and leaves the revolver centered on the table, a chilling closure that leaves their fates uncertain and the lodge steeped in a grim, unsettled silence.
