Emma visits her boyfriend, Austin, and his father, Tommy, who is the coroner in their small town. Tommy explains to her that coroners in the past used to tie bells to bodies to make sure they were actually dead, not comatose. The sheriff arrives with the mysterious body, dubbed Jane Doe, and tells Tommy that he needs the cause of death by morning. Austin postpones his date with Emma to help Tommy, promising to meet her later that evening.

Tommy and Austin perform the autopsy on Jane Doe and quickly become confused by what they find. There are no external visible signs of trauma, but her wrist and ankle bones had been shattered. As well, her tongue has been crudely cut out, one of her molars is missing, her lungs are blackened as though she had suffered third degree burns, and her internal organs reveal numerous cuts and scarring. Jimsonweed, a paralyzing agent not native to the area, is found in her stomach. The condition of much of the body suggests that death had just occurred, while cloudiness of the corpse’s eyes suggests that she had been dead for a few days.

Other mysterious events occur. The radio begins to spontaneously change stations, frequently settling on the song "Open Up Your Heart (And Let the Sunshine In)", and Austin hears sounds and believes he sees people standing in the morgue's hallway. He also finds their cat mortally wounded, hiding in an air duct.

News reports on the radio state that a severe storm is about to hit the area, but Tommy and Austin decide to stay and finish the autopsy.

Tommy finds the woman's missing tooth wrapped in a piece of cloth in her stomach. The cloth has Roman numerals and letters as well as an odd diagram. Similar symbols are found on the inside of her skin. The lights in the room suddenly explode. During the confusion, they realize that other corpses in the morgue have gone missing. They decide to leave, but the elevator does not work and a fallen tree is blocking the exit door. An unseen figure attacks Tommy in the bathroom, leaving bruises on his body.

Austin and Tommy decide to burn Jane Doe's body. Unable to get to the cremation furnace, they set her ablaze in the exam room. The fire spreads rapidly; Tommy puts it out with an extinguisher but is disturbed to find the body has not burned. When the elevator turns back on, Tommy and Austin try to use it to escape but the doors will not close. Panicked, Tommy uses an axe against what he believes to be one of the animated corpses. When he and Austin exit the elevator, they discover he has actually killed Emma, who had returned to pick up Austin for their date.

Certain that Jane Doe's corpse has been preventing them from finding out the truth about her death, they return to the examination room. Tests determine that Jane Doe's brain tissue cells remain active, proving that she is somehow still alive. Further examination of the cloth determines that the markings refer to Leviticus 20:27, which condemns witches, and the year 1693, the date of the Salem witch trials. Tommy and Austin reason that in their attempt to punish a witch, the Salem authorities instead transformed an innocent woman into a witch who now wants revenge. Tommy offers himself to the corpse as a sacrifice, hoping that she will spare Austin. Tommy’s ankles and wrists shatter, mimicking the wounds on the corpse. Tommy forces his son to 🤬 him to end his misery, Austin reluctantly stabs his father on the chest with knife. Believing he hears the sheriff outside, Austin tries to flee but realizes the voice is another hallucination. Startled by a vision of Tommy's corpse, Austin trips over the railing and falls to his death.

The police arrive the next morning and are again confused by another inexplicable crime scene. The corpse, showing no signs of an autopsy, is taken to another county. During the ambulance ride, the radio begins to play "Open Up Your Heart (And Let the Sunshine In)", the camera moves across her body settling on her feet, her big toe twitches.