In 1986, a young Adelaide Thomas goes to the beach while on vacation with her parents in Santa Cruz. She wanders off on her own and enters a funhouse, where she encounters a doppelgänger of herself in the hall of mirrors. Adelaide is later reunited with her frantic parents, although traumatized and unable to talk about her experience.
In the present day, an adult Adelaide heads to her family’s beach house with her husband Gabe and their children, Zora and Jason. While the family is at the beach with their friends the Tylers, Adelaide is distracted by a series of strange coincidences. Jason wanders off and finds a stranger dripping with blood. Adelaide notices his absence and panics, eventually cutting the outing short after she finds him.
Agitated by the day’s events, Adelaide confesses her childhood trauma to Gabe and says she wants to leave. Before anything can be done, the power abruptly cuts out and they see a group of four people dressed in red jumpsuits standing silently outside the house. Gabe attempts to confront the intruders, only for them to attack and break in. They then reveal that they are doppelgängers of the Wilsons, and call themselves “the Tethered,” as they are all mentally linked to partially mimic the actions of their originals.
The family is separated by their opposites. Adelaide is chained to a table by Red, Zora is pursued out the house by Umbrae, Gabe is dragged outside by Abraham, and Jason is taken into a closet by Pluto. Zora manages to get away from Umbrae when she kills a neighbor. Gabe and Abraham fight on the family’s newly bought boat, with Gabe eventually managing to kill his double. Jason notices that Pluto mirrors his actions almost exactly, and traps him in the closet after distracting him with a magic trick. When Red hears Pluto banging on the walls, Adelaide is left alone and manages to break away from the table. The family regroups and escapes on the boat.
Meanwhile, the Tylers are attacked by their doubles, the twins getting stabbed, and die instantly, Josh is stabbed in the chest, dies instantly, Kitty is stabbed but survives, and tries to crawl to Josh’s doppelgänger for mercy but is murdered by his Tethered with her throat being slit. Shortly after, the Wilsons arrive at their beach house looking for help and encounter the Tethered Tylers. A fight ensues, with the Wilsons triumphing. Realizing their situation is not unique, they turn on the news and learn that the Tethered have been killing their opposite selves all over, and are subsequently joining together to hold hands and form a massive human chain. Gabe wants to stay in the Tylers’ house and ride out the crisis, but Adelaide insists they stay on the move and head for Mexico.
Umbrae reappears as they drive away in the Tylers’ car, but Zora manages to shake her off, killing her. As morning comes, the family arrives at the Santa Cruz boardwalk, where their way is blocked when Pluto sets their own car on fire in the road. Seeing that Pluto still mirrors his every move, Jason walks backward, causing Pluto to do the same and burn to death. Red then reappears and abducts Jason. Adelaide pursues them while Gabe and Zora find an abandoned ambulance. All of them witness the Tethereds’ human chain, leading from the sea across the boardwalk and town.
Adelaide returns to the boardwalk funhouse, discovering a secret tunnel in the hall of mirrors. The tunnel leads further and further downward into a massive complex filled with rabbits. Adelaide eventually comes upon Red, who claims that the Tethered were created by the government in an attempt to control the populace, but were then abandoned underground when the experiment proved a failure. For generations, the Tethered were trapped beneath the Earth, doing nothing but mimicking the actions of their counterparts aboveground. Red reveals she is the mastermind behind the Tethereds’ attacks on the surface, and that she’s believed she was chosen by God to lead them to do this ever since her encounter with Adelaide in 1986. The two fight and Adelaide manages to kill Red.
The family reunites and drives away in the ambulance. As they leave town, Adelaide has a flashback. The night Red and Adelaide met in the funhouse, Red knocked Adelaide out (crushing her larynx in the process), chained her to her own bed in the underground complex, swapped their clothing, and took Adelaide’s place in the surface world. “Adelaide” was the doppelgänger all along. Having seen his mother act similarly to the Tethered in the throes of fights, Jason appears to realize this. The final scene shows the Tethereds’ human chain stretching unbroken over the countryside into the distance.
Lupita Nyong’o as Adelaide Wilson (née Thomas), the matriarch of the Wilson family, Gabe’s wife, and Jason and Zora’s mother.
Winston Duke as Gabriel “Gabe” Wilson, the patriarch of the Wilson family, Adelaide’s husband, and Jason and Zora’s father.
Shahadi Wright Joseph
Shahadi Wright Joseph as Zora Wilson, Jason’s sister, and Gabe and Adelaide’s teenage daughter.
Evan Alex as Jason Wilson, Zora’s brother, and Gabe and Adelaide’s son.
Elisabeth Moss as Kitty Tyler, a friend of the Wilson family, Josh’s wife, and the mother of Gwen and Maggie.
Tim Heidecker as Josh Tyler, a friend of the Wilson family, Kitty’s husband, and the father of Gwen and Maggie.
Yahya Abdul-Mateen II
Yahya Abdul-Mateen II as Russell Thomas, Adelaide’s father.
Anna Diop as Rayne Thomas, Adelaide’s mother.
Cali and Noelle Sheldon
Cali and Noelle Sheldon as Gwen and Maggie Tyler, Kitty and Josh’s twin daughters.
Storyline Credit: Wikipedia