The film follows Dennis Peterson (Frederick Koehler), a special-needs brother who lives with his brother and caretaker, John (Sean Patrick Flanery). John loves Dennis, but is getting increasingly stressed over the difficulty of taking care of his brother, combined with the stress of his girlfriend, Lydia (Dina Meyer), and Mildy Torres (Kim Darby), a social worker, who are both pressuring him to put Dennis is a state home, albeit for different reasons. Dennis suffers from incredibly vivid nightmares with uncertain beginnings and ends, where he is fully articulate, and pursued by a cadaverous figure (Michael Berryman). John puts an antique mirror, found in a Prohibition Vault in the basement, into Dennis's room and Dennis, recognizing the mirror from his dreams, begins talking to it, and it begins to talk back, telling him that he's being tested and that he needs to prove himself... by killing.
This film should not be confused with the video game series, The Evil Within.
This film exhibits the following tropes:
- Animal Motifs: Spiders.
- Catapult Nightmare: This is how Dennis awakes from several of his nightmares. In a few cases, he even actually woke up...
- Dead Guy Puppet: Dennis kills Lydia and turns their body into a puppet.
- Department of Child Disservices: Mildy openly tells John that she doesn't think he is capable of properly taking care of Dennis, and baits him with the "symptoms" of lack of patience and temper, acting as if the fact that he's angry that she's accusing him of not being adequate means he's suffering too much stress from taking care of Dennis. She also claims anonymous complaints, over events that could only be seen from within the house, for her justification for this badgering.
- Mirror Monologue: The film has Dennis doing several of these as he discusses his inner thoughts.
- Nightmare Sequence: Dennis points out at the beginning of the film that dreams follow an illogic that always reveals itself when you try to explain them. The problem is, some of his nightmares, while horrific and surreal, make perfect sense, and are a continuing story...
- Taxidermy Is Creepy: One of the clues that John gets of Dennis's activity is his sudden interest in taxidermy videos.
- The Man in the Mirror Talks Back: The film takes pains to only imply this via camera angles and conversation shifts, but Dennis certainly believes that his reflection is someone else. He appears to be right.
- Your Worst Nightmare: The Cadaver stalks Dennis through his dreams, and seems to be taking him over bit by bit.