After the death of their father, estranged sisters Lizzie and Jo are back together under their mother's roof on the night of the winter formal. Jo chooses to go out with her friends while Lizzie isolates herself, unable to think about fun at a time like this. After her sister Jo decides to have her Senior Formal party at the house, Lizzie has to dodge Jo's friends and her own mom who is worried about her mental health. But Lizzie won't be alone for long, once an evil force tries to make contact through her bedroom mirror. Ostracized by Jo and her friends after an argument, Lizzie retreats to her room - only to find herself following in her father's fatal footsteps as the evil entity behind the mirror called Mira closes in and possesses Lizzie. Now having lost control of her own body, Lizzie sets out to feast on the inhabitants of the house, one by one. As the body count mounts, Lizzie learns the secret to Mira's plan and how could it also be a way to stop her. Realizing they're being hunted, the survivors find a cryptic message in the mirror. Carrie and Jo have a mother/ daughter breakthrough, which might be able to save Lizzie and bring their family back together. While Nora makes a break for it, the rest of the family hunts down the mirror that must be the source of their suffering with hopes of shattering it to set Lizzie free. Mira taunts Jo and Carrie, but the family holds onto the hope that they can break through to the real Lizzie. The evil within the mirror then loses its grip on Lizzie and needs a host to survive, but unleashes something more terrifying. In a final confrontation with Mira, Jo sacrifices herself and takes Mira back to her world, trapping her inside, and leaving Lizzie. The story ends with Lizzie promising to find a way to save Jo.