NOTE: This spoiler was submitted by Joshua
The film begins with a family of four being on vacation and having a cookout with some friends. While the parents talk about life and how fast their kids grow up and enjoy the food, Andrew (the teen son of the other two parents) decides to explore the canyon with Stephanie and Michael (the teen daughter and the young son of the main parents). All the parents then talk about Bear Grylls for a good minute after cautioning their children to be careful.
The three children then explore and say that the place could be scary. Andrew then tells Mikey about how the Grand Canyon was haunted and legend told of guardians of the spirit world once lived in the trees and would come back eventually and end the world. Andrew and Stephanie then decide to explore further, with Andrew giving Mikey his watch after Mikey gets scared from the story. While just sitting there, Mikey drops Andrew's watch and jumps down a rock to get it, only to be sent falling inside the Grand Canyon. Inside, an unharmed Mikey finds several black rocks with symbols in the middle and pockets them into his backpack without anyone noticing.
Both families then go home. The next day, Mikey's parents (Kevin Bacon and Radha Mitchell) attempt to have sex, but are interrupted by a random door banging and a dog barking. When the mom goes downstairs, she sees that the tap is on. She thinks it's Mikey, but when she asks him, he claims "Jenny" did it and not him. When she asks who Jenny is, Mikey claims it's his friend in the walls. She then tries to talk to her daughter, but Stephanie just freaks out at her mom 'invading her privacy' (even though all she did was look in the mirror) and closes the door. When the mom then goes back to find Mikey having breakfast, the tap is open again. The dad and Stephanie then decide to go off to work and school, but when the dad tries to touch Mikey's backpack (with the rocks), Mikey freaks out and just tells his dad and sister to go. Mikey then plays hide and seek with his mom by hiding in plain sight under a blanket and jumpscares his mom when she finds him.
Mikey and his mom then go grocery shopping and Mikey goes off to the balloon section and "worries his mom sick". Mikey then gets two balloons, and they head home. At home, while Mikey is coloring and his mom is on her laptop, she hears thumping in the attic. She then goes up and gets jumpscared by Mikey. When she asks Mikey how he got up, he claims Jenny taught him how to. The lightbulb then pops, and she goes down with Mikey.
At work, Mikey's dad is working and talks with a new employee (who is then later implied to be having an affair with him despite only appearing once). Mikey's dad and Stephanie then get back home. Later that night, Mikey's mom overhears the dad talking about work and then walks around the house. Stephanie, who is taking a shower, is suddenly surprised by handprints appearing on her mirror. Thinking it's Mikey, she storms off to his room and threatens to ruin his toys. Mikey then claims that it was Jenny and the two fight. The fight is broken up by Mikey's mom and comforts Mikey. Mikey's dad talks to Stephanie, and we find out Mikey is autistic. Stephanie tells him to get out. Later that night, Stephanie wakes up to find black handprints on her blanket. Ignoring it, she goes down to get a snack and gets surprised by something banging the microwave. In fear, Stephanie goes to her parent's room and sleeps there instead.
The next day, the dog continues to bark, and we find out it's the neighbor's dog and Mikey's mom finds a black handmark on Stephanie's blanket and disinfects the air in the room. Stephanie then has a container in her room where she vomits into (because of anorexia) and freaks out when she sees her mom watching. When Mikey's dad gets home, a crow lands on his car, and he shoos it. Inside, he breaks up a fight between Mikey's mom and Stephanie and puts Stephanie out of the room. We then find out that her anorexia has caused multiple containers of vomit under her bed. Mikey's dad then takes her to a therapist to get help.
The next day, Mikey's mom dumps him at his grandma's house while she decides to go to the hospital for Stephanie. At his grandma's, Mikey tries to follow her pet cat to the living room. The door then jumpscares Mikey's grandma and the water turns on. When she shuts off the tap, a snake is suddenly on the kitchen counter. We then see Mikey's parents running to the hospital where we learn that no one was harmed, but Mikey tried to kill his grandma's cat.
Later at home, Mikey is sitting alone in his room feeling the rocks in his backpack. His mom, who is checking herself in the mirror, suddenly sees a blanket with a figure in it. Thinking it is Mikey, she touches it, and it sinks into the floor. The fire alarm then goes off (and the figure in the blanket rises again), and she sees a fire in Mikey's room, while Mikey is in the hallway holding a box of matches.
When Mikey's dad Peter gets home, Mikey gets scared and runs up to his treehouse. Mikey's dad is fed up with Mikey's autism, saying he is now dangerous. We then hear something coming from the big scorched part of Mikey's room.
Later that night, Peter is talking to someone on the phone for business and hears a weird noise in the garage. There, the garage door is open. He closes it. He then goes back inside and sees the office door is open. He closes it. The TV then jumpscares him and he turns it off. We then see Mikey in his room aligning the rocks and hearing something from the scorched wall. Mikey's mom (who is taking a bath) is also jumpscared when something suddenly thumps while she's in the bathtub.
The next day, Peter and Mikey's mom talk about the strange events. Mikey's mom then googles and finds out about Anasazi Indians. These Indians believed that demons were bound to rocks and that if taken, they would connect to young children who would trigger 'The Darkness'. The only way to get rid of it is to put the rocks back to where it was, but by someone who was not afraid of the events. She then sends the video to Peter and Peter sees a news article about how evil beings latch to autistic children. Peter's boss then jumpscares him by walking into the office during the "Let's go on the Internet and find answers" montage. Mikey's mom then goes to the supermarket and buys vodka along with some toys for Mikey.
Mikey's mom Bronny, and Peter then go out for dinner with Peter's boss and his wife. They have small talk about business, and then the boss's wife talks about the supernatural before being cut off, and Peter is visibly embarrassed when his wife indulges her. Meanwhile at home, Mikey walks off somewhere while his sister is listening to music and plays with the rocks while looking at the burn stain.
When Bronny and Peter get home, they fight over his embarrassment over her. When Bronny finds Mikey, he is covered with black handmarks and foams blood from his mouth. Peter checks Mikey, but Mikey is alright. Later that night, Bronny wakes up and hears Mikey counting. She then walks down the hallway and finds their family picture from the Grand Canyon shattered. She then sees Mikey with his back facing her counting after being led there by a wolf silhouette. Inside, she asks Mikey who he's talking to. He claims it's the Sky People. She asks where they are. He says it's behind her. Bronny screams and wakes up since it was a dream. She wakes up, and so does Peter. Mikey also wakes up, and so does Stephanie. But the neighbor's dog is there and attacks Stephanie. Peter runs out and screams at his neighbor (who is also somewhat awake late at night) about the dog. They then take Stephanie to the hospital and Mikey watches a movie with things exploding and is entranced by it.
When Peter gets home, the neighbor's dog is now muzzled. Later that night, Mikey is still playing with his rocks. Hands then come out of the big scorched stain on his wall after he asks if Jenny is there. Bronny and Peter then have an argument, and she cries and confronts him about an affair. Peter then packs his things and asks for time off from his boss, telling him about the weird things at home. His boss then suggests Teresa, a woman who performs spiritual healings.
Peter then continues to research over the supernatural beings and rewatches the video Bronny sent him (but this time the footage is extended to provide more backstory over the haunting) and finds out that the hauntings cause rifts amongst loved ones and the whole story of the haunting. He then emails his boss for contact details about the spiritual healer.
At home, Bronny gets drunk and looks at family photos while crying.Peter then comes home and hears noises coming from the treehouse and arms himself with a badminton racket. In Mikey's room, two figures rise from sheets, and he asks if it is Jenny. Stephanie then notices her bathroom door open before the black hand marks appear all over her body and begin choking her. Peter then gets jumpscared by a coyote which then runs into the house. Bronny then notices a figure behind them in the Grand Canyon photo. Peter storms into Stephanie's room and gets her out. He then sees Mikey in the bathroom with him smiling and the ceiling being covered with red handprints instead of black.
Peter then takes his entire family and go to a hotel (where they buy the presidential suite out of desperation since only one room is left) where Bronny and Peter then reconcile and pledge to stop the haunting together. The next day, they find Teresa and Gloria (her translator). They talk about the hauntings, and they begin to do a spiritual clearing of the house. Upon arriving in Mikey's room, they note that it's where the real evil is. They then begin chanting but the demonic forces attack and drop a chandelier. Mikey then gets away from them and tries to enter the portal. After some more supposedly scary moments, Peter runs up to Mikey's room and locks the door.
He sees Mikey walking into the portal with the demons. To stop them, Peter tries to bring the stones in, but he's afraid. He decides to swap with Mikey and begins walking away with the demons, but Mikey picks up the stones and claims that he's not afraid. The demons then all leave and Peter/Mikey jump out of the portal together. After everything is normal and the house is cleansed.
Everyone is happy, and the family then has a picnic at the end. Roll credits.