The movie opens with a security guard running away from an unseen force. He is killed when his reflection slits its throat the guards throat opens with the same wound.
Ben (Kiefer Sutherland), is an ex-cop in NYC who was fired after he accidentally shot another cop. His wife has kicked him out because he was drinking and hostile due to the stress of being fired and killing someone. Ben lives with his sister, (Amy Smart).
He takes a job as a security guard, guarding an old burned out building that was once the most classy shopping center in New York. He finds out the the former security guard was the one who had his throat cut. The security guard prior to that one had supposedly killed his whole family and burnt the shopping center to the ground (killing 45 people). He claimed that he was trying to destroy the mirrors in the shopping center because the mirrors had killed his family.
Ben starts seeing strange things while at work and investigates the history of the shopping center. It was once a hospital for the insane run by a mad doctor in the 1950's. Ben follows clues and finds that the mad doctor had treated a 12 year old girl for multiple personalty disorder by leaving her in a round room of mirrors for days. On the girls final day in the room "something" came out of her body and was absorbed into the mirrors. The girl was sent home and the entity started killing the people in the hospital and the doctor. The girl was sent by her family to live in a place with no mirrors (a convent) so the entity couldn't find her.
Ben's sister is murdered by the entity while in the bath tub, it rips her jaw off while Ben is out investigating. Ben fears for his wife and two kids safety and goes to look for the woman at the convent , she is very old. He takes her back to the round room of mirrors under the burnt down shopping center in hopes of saving his family from the entity which is now stalking them. Once the old woman is placed in the room of mirrors the room explodes ripping her apart.
Meanwhile the entity attacks his family through mirrors, pulling his son into his reflection in water on the floor, he nearly drowns, his daughter nearly has her throat slit by the fake reflection of her mother.
Back at the mirror room Ben fights the entity and seemingly wins and walks out of the shopping center onto a street loaded with police cars and people. He feels at peace and happy knowing his family is safe now. Suddenly he notices that the writing on cars and signs is backward.
He is dead and seeing things as reflections from the other side of the mirror.