Kate, the protagonist, is a struggling nurse who agrees to attend her estranged sister Anne's bachelorette party at the behest of their dying father. Anne's fiancé, Kevin, has booked a remote cabin through a home-sharing app, and the five sisters arrive for what is meant to be a fun weekend away.
However, things quickly take a dark turn. The sisters discover that the cabin is situated in an isolated, wooded area, and their phones have no signal. Moreover, Kevin and his friends are revealed to be arrogant and obnoxious, frequently mocking the sisters and belittling Kate for not having a partner.
As the night wears on, the sisters start to feel uncomfortable and unwelcome. They discover a stash of creepy toys and a strange shrine in the cabin, hinting at Kevin's dark past. After a heated argument, Kevin and his friends leave, promising to return in the morning to take the sisters back to civilization.
But the sisters are not alone. A masked figure begins stalking and attacking them, one by one. Kate and Anne team up to fight for survival, using their wits and ingenuity to outsmart the killer. As the night wears on, they uncover shocking secrets about their own family, including long-buried feuds and betrayals.
In the end, Kate emerges as the last woman standing, having successfully dispatched the killer and saved her sister. However, the trauma of the night proves too much for her, and she is left to grapple with the revelation of dark family secrets. The film ends on an ambiguous note, with the suggestion that Kate's battle is far from over.