Una familia se dispone a ir a la playa y disfrutar del sol.
Jason, el más joven de la misma, desaparece.
Cuando sus padres le encuentran, el niño parece estar desorientado.
Esa noche, una nueva familia trata de aterrorizarles y lo consiguen cuando se dan cuenta de que son físicamente y emocionalmente iguales.
A young Adelaide (Madison Curry) goes to the beach on a trip with her parents Rayne and Russell (Anna Diop and Yahya Abdul-Mateen II).
After Russell wins Adelaide a Thriller T-shirt at a carnival game and plays Whac-a-Mole,
Adelaide wanders off and encounters a man with a Jeremiah 11:11 placard and then walks into a nearby fun-house. Inside, she’s terrified by the mirrors and vibe of the place and eventually comes face to face with an exact doppelganger.
The incident scares her. Some time later, Adelaide is refusing to talk as her parents worry about her. The therapist tells them to make Adelaide tell her story through the form of anything – reading, writing, or dance.
Many years later, an adult Adelaide Wilson (Lupita Nyong’o)
goes on a beach trip with her husband Gabe (Winston Duke) and their two children Zora (Shahidi Wright Joseph) and Jason (Evan Alex).
While the family has lunch at their beach house, we find out several things –
one is that the beach trip was to help the children cope with the death of their grandmother and the other is that Adelaide appears to still be terrified of the idea of going to the beach because of what happened before and refuses to go.
After some persuasion, however, she reluctantly agrees to join her family to go to the beach.
On the way, the family sees a man being brought into an ambulance – it is the same man that Adelaide encountered many years ago with the Jeremiah 11:11 placard.
At the beach, the Wilson family meets their friend the Tylers, comprising of Kitty (Elizabeth Moss), Josh (Tim Heidecker),
and their twin teenage daughters Gwen and Maggie (Cali and Noelle Sheldon). While the kids are all at the beach, Kitty and Adelaide talk about Adelaide’s soft-spoken nature and her past as a young ballet dancer.
Jason soon wanders off on his own and finds a man with his arms stretched out dripping with blood. Adelaide notices her son missing and panicking,
eventually finds Jason and decides that it’s time for the family to go back to the house.