Los Angeles, 1967
Mr. Browning (Sam Anderson) and his younger wife Jenny (Kate Siegel) are at the home of Alice Zander (Elizabeth Reaser), a fortune teller. Alice gathers the couple around a table for a seance. Mr. Browning wants to speak to his deceased wife and ask her questions. Jenny isn't convinced and thinks they're getting ripped off. When Mr. Browning asks about giving money to Jenny, something that supposedly represents his dead wife's spirit creeps behind the curtains and lunges out toward them. Mr. Browning is frightened beyond belief. He attempts to pay Alice, but she declines out of guilt.
The spirit is actually Alice's teenage daughter Paulina (Annalise Basso), while her younger daughter Doris (Lulu Wilson) was hiding to create the effects of candles blowing out. Alice scolds Lina for scaring Mr. Browning and costing them their pay, but Lina defends her actions because she thinks Jenny was a bitch. Alice agrees.
Lina sneaks out at night to go to her friend Ellie's (Halle Charlton) house. The two of them, plus Lina's boyfriend Mikey (Parker Mack) and other friend Betty (Alexis G. Zall) play with a Ouija board game. They try to contact a spirit, which creeps the hell out of Betty. Ellie's mom bursts through the door, making Betty scream. Alice later picks up Lina, upset with her.
While the girls are at school, Alice goes to find a Ouija board of her own after Lina suggests it could be good for business. At night, Alice uses the board and unknowingly makes contact with a spirit named Marcus, who speaks through Doris. Doris responds to Alice's questions, to Lina's confusion.
Doris uses the Ouija board on her own - despite the first rule of the game being not to play alone - in the hopes of making contact with her dead father Roger (Michael Weaver).
At school, Father Tom (Henry Thomas) calls Alice in to review Doris's homework. It's all written in cursive, despite no one having knowledge of Doris ever learning how to write like that.
Alice and the girls return home to find a notice of foreclosure on their door. Doris returns with a pouch full of money that she claims Roger told her about. She shows her mom and sister a space in the basement wall that contained the money. Later, Doris shows Alice and Lina how she communicated with Roger. To their astonishment, the planchette moves on its own when Alice asks the spirit where Roger was when she told him she was pregnant with Lina. The planchette moves around to spell "SHOWER". When Alice asks if Roger is really there, it moves to YES. The girls look through the planchette lens to see if they spot anything, but Lina is too freaked out to keep looking.
Alice starts to keep Doris home from school to work with her. Using the Ouija board, they have been generating more business, as customers are convinced with Doris speaking in voices that aren't hers and is answering questions only the deceased would know. Doris later starts to experience a pain in the back of her neck. After Lina gives her medicine, Doris looks through the planchette in the mirror and sees a tall, black spirit with its mouth sewn shut. Doris screams, and the spirit sticks its arm down her mouth as it possesses her.
Alice goes out with Father Tom for the night while Lina has Mikey come over as Doris watches TV. Tom chooses not to pursue other relationships after his wife's passing, as well as to keep with his faith. Lina and Mikey spend a brief time together and only kiss before she kicks him out. As Mikey is leaving, Doris startles him as she appears out of nowhere. She then starts to describe being strangled to death in graphic and disturbing detail.
Lina brings a bunch of papers written by Doris to Tom at school. They are written in Polish, and Tom says he knows someone at the school who can translate them for her.
In the schoolyard, two boys that make fun of Doris are sitting on a bench when one of them aims his slingshot at her head. Doris turns around and stares the bully down and causes the kid to strike himself in the face.
Lina finds one of her dolls has what look like stitches drawn onto its mouth. She confronts Doris about it, but Doris claims it was their dad that did it to "stop the voices".
Tom visits the Zanders for a seance with Alice and Doris. He tries to have them make contact with his deceased wife Gloria. He asks what Gloria's middle name was. The planchette moves around to spell Lynn. It then moves around to indicate a fight that happened between them that Gloria forgives Tom for. Doris also makes a voice that sounds like a grown woman. Tom then brings Alice and Lina upstairs to tell them that Gloria's real middle name was Catherine, and that he tried to manipulate the entity into doing what it did. He then explains to the ladies what Doris wrote in her letters - it's a journal entry from Marcus about a man they called the "Death Doctor", who tortured people in that house with his experiments.
Mikey shows up downstairs for Lina, and Doris greets him. She takes him to the basement to show him something "cool". He sticks his hand in the spot where the money was found. A mouthless skull pops out. Doris's eyes go demonic and she starts rapidly whispering something into Mikey's ear. Alice, Lina, and Tom go downstairs and see Mikey's body drop with a noose around his neck. Lina freaks out, but Alice tells her to calm down and find Doris.
The three take the Ouija board downstairs to burn it in the furnace. They discover the skull, as well as other bones from the people described in the journals, which means they were playing in a graveyard this whole time (which is against rule #2). The phonograph in the basement turns on, and they hear Doris screaming. Tom crawls through a vent and finds Doris. She attacks him with supernatural force and causes him to break his neck as he is flown down the stairs.
Upstairs, Alice and Lina find the Ouija board intact on the table. Alice is grabbed by an unseen force, while Mikey's corpse swings by and grabs Doris, throwing her to the stairs. Doris appears and starts whispering things into Lina's ear. Alice pleads with the spirits to take her instead of her daughters. The voices say they'll take all of them.
Lina is pulled into her bedroom the day she confronted Doris about her doll. She sees her father and understands now what Doris meant by "stopping the voices".
Alice is being dragged in the basement. Lina faces off Doris and the spirits. The spirits try pulling Lina away as she reluctantly sews Doris's mouth shut. When she is done, Doris appears normal and wakes up. She is pulled up by Roger. In reality, Alice and Lina cry over Doris's body. Lina is momentarily possessed and she stabs Alice. When she reverts to normal, she tearfully begs her mother for forgiveness, but Alice says she knows it wasn't her. She sees Roger and Doris standing behind Lina before she dies.
Two months later, Lina is in a mental hospital talking to Dr. Fuller (John Prosky) about what happened to Doris's body. In her room, Lina makes her own Ouija board on the floor with her blood and an eyeglass to contact Doris. Fuller passes by Lina's room and sees what looks like Lina and Doris sitting next to each other on the bed. When he turns to look back, he just sees Lina staring at him. He doesn't see Doris running on the ceiling toward him...
After the credits, we see an old Lina (Lin Shaye) in her room as she is told someone claiming to be her niece is there to see her (just like the first movie).