Plot
A young woman in the woods is captured and held hostage in the cellar of a remote cabin, where an old woman recites incantations from a book in the Welsh language. The young woman begs for her mother before revealing her demonic possession. Her father, Harold, sets her ablaze before shooting her dead.
Some time later, David, his girlfriend Natalie, and their dog Grandpa arrive at the cabin, which is his family's holiday home. They reunite with David's estranged younger half-sister, Mia, and their friends, high school teacher Eric and nurse Olivia. They plan to stay in the cabin while Mia overcomes her heroin addiction. Olivia tells David that this isn't Mia's first attempt at quitting, and Eric adds that Mia's last attempt resulted in her relapsing and legally dying before being revived.
David discovers that the cabin had been broken into, finding the cellar littered with rotting animal corpses, a worn double-barrel shotgun, and a book called the Naturom Demonto. Eric reads an incantation from the book, awakening a malevolent force. Mia begins seeing a demonic doppelgänger of herself in the woods and tries to leave using Eric's car, crashing into a nearby swamp, and is chased by the demon. She is trapped by vines that sexually assault her, and she is possessed.
David finds Grandpa beaten to death, and discovers Mia scalding herself in the shower with boiling water. David tries to take Mia to a hospital, but is forced to return to the cabin due to flooded roads. Olivia administers Mia a sedative, knocking her out. Later that night, Mia wounds David with the shotgun and vomits into Olivia's mouth before being locked in the basement by Eric. A now-possessed Olivia mutilates her face and stabs Eric before he bludgeons her to death. Mia lures Natalie into the cellar and bites her hand before slicing her own tongue.
David rescues Natalie, and Eric explains, per the book, that the Taker of Souls must claim five souls to unleash the Abomination. He further explains that to stop Mia, they must purify her by either live burial, dismemberment, or burning. Meanwhile, Natalie's wound becomes infected, causing it to become possessed. She attempts to amputate it with an electric knife, causing a power outage in the cabin. Natalie, now fully possessed, attacks the pair with a nail gun, but David shoots her other arm off; Natalie bleeds to death from her injury.
David begins dousing the cabin in gasoline, but decides to bury Mia instead. He digs a grave but Mia tries to drown him, and Eric is fatally stabbed saving him. David sedates and buries Mia but after hearing her heartbeat stop, digs her back up and attempts to resuscitate her with a homemade defibrillator; bringing her back to life. Furious at being driven out of Mia and so close to being resurrected, the wrathful Taker of Souls is forced to possess the corpse of Eric before attacking David in the cabin when he comes to retrieve his car keys. David shoots a gasoline can, sacrificing himself to defeat the possessed Eric.
With David's death being the fifth claimed soul, blood begins to rain from the sky and the Taker of Souls rises as the Abomination. During the ensuing battle, Mia manages to sever the Abomination's legs with a chainsaw obtained from a tool shed, but it overturns David's Jeep onto her left arm, crushing it in the process. After Mia's hand is torn off while freeing herself, she bisects the Abomination's head and torso with the chainsaw before it sinks back into the ground and the blood rain ceases. An exhausted Mia leaves, unaware the Naturom Demonto is still intact.
In a post-credits scene, an older Ash Williams (the protagonist of the original three Evil Dead films) is seen in shadowed profile. He says his signature catchphrase, "Groovy."
