TRAILER
During an exorcism ritual, the possessed Hannah Grace almost kills the priest by choking him while suspended in mid-air. Her father, Grainger, then suffocates her to death using a pillow. As her father sobs over her dead body, a fly lands on her hand and it twitches ominously.
Three months later, Megan Reed, an ex-cop with the Boston Police Department struggles with depression and an addiction to pills after her patrol partner was shot dead by a criminal whom she failed to subdue. Megan's friend Lisa Roberts finds her a nightshift job in the Boston Metro Hospital's morgue, located in an intimidating brutalist architecture building (portrayed by Boston City Hall). During Megan's second shift, a man (later identified as Grainger) aggressively tries to convince her to let him into the building, but she denies him and informs the two security guards Ernie Gainor and Dave. However, shortly after, Megan helps EMT Randy to move the corpse of a brutally murdered young woman (later identified as the one of Hannah Grace) into the building and the man secretly enters. Randy tells Megan a man stabbed Hannah to death and was then caught in the act trying to burn her body in an alleyway.
When Megan tries to fingerprint and photograph Hannah's corpse, the camera explodes and the fingerprints return as illegible by the computer. Other strange things occur and Megan becomes more suspicious of the corpse. Megan soon encounters Grainger trying to drag Hannah's corpse through the building. Alongside Ernie and Dave, Megan manages to subdue Grainger. The latter screams Hannah's corpse must be burnt because she isn't really dead, but they do not listen to him and have him arrested by the police.
Megan's ex-boyfriend, Andrew Kurtz, is still employed as an officer and responds to the scene. He agrees to help Megan identify the corpse. Soon after, Andrew tells Megan that Hannah Grace had died three months earlier and asked Megan whether the given finger prints was Hannah's. Megan confirms this, and Andrew thinks maybe there is some error in the computer data. Meanwhile, Hannah kills Dave by telekinetically lifting him across the ceiling and into her refrigerated drawer in the morgue where she breaks his body. Soon after, Megan notices that some of the wounds on Hannah are missing, as if it had healed by itself. Investigating the security footage, Megan sees a glimpse of Hannah's corpse crawling around in the building. She shows the footage to Lisa, who does not believe her and accuses her of having a relapse on her addiction to pills. Lisa is killed by Hannah soon after. When Randy returns to the morgue to deliver another corpse, Megan shows Randy the healing body of Hannah.
After Randy leaves the morgue, Megan notices that the lift closes by itself and is going down. Megan investigates the security footage and sees a glimpse of Hannah's body crawling inside the lift. She rushes down to the access bay to warn Randy, but Hannah has already killed him. Suddenly, Andrew calls Megan to warn her that Grainger has escaped police custody after killing the two officers transporting him. Moments later, Grainger forces Megan to take him to Hannah's body at gunpoint. Grainger explains to Megan that he is Hannah's father. He tells her that numerous exorcisms failed because the demon possessing her was too strong, and that it is able to possess Hannah's body after her death by killing people to heal itself. He tells her that Hannah had depression and it worsened until the demon was able to enter Hannah's body. The blue eye colour is the sign of the demon possessing Hannah. Grainger wonders why Hannah killed Dave and Lisa, but did not kill Megan. Megan agrees to help Grainger cremate Hannah, but she reanimates and pushes Grainger into the fire. Then she locks Megan inside her refrigerated drawer.
Andrew and Ernie come to Megan's aid. Hannah kills Ernie and then tries to kill Andrew, but Megan forces herself to be calm. She picks up Andrew's firearm and shoots Hannah, then drags her to the crematorium while Andrew calls for backup. After a brief struggle before the incinerator, Megan pushes Hannah into the fire.
Megan recounts how she has managed to stay clean for over two months. As she looks into the mirror at her reflection, a fly lands on the mirror's surface. Megan smashes it with her hand.
