Barb awakes in a deserted, decaying pool, its emptiness echoing with her screams for Nancy. Frantically, she tries to scale its crumbling edges, but is suddenly yanked under by an unseen force.
Joyce decorates her home with festive Christmas lights, creating a secret language with Will. By toggling them on and off, they communicate, with Will revealing his ability to control the glow.
Dr. Martin Brenner, the director of Hawkins Lab, grudgingly allows Hopper and his deputies to peruse the lab's security footage, hoping to prove Will's innocence. But Hopper's sharp eye quickly detects the deceit, realizing the footage is a sham. Determined to get to the bottom of things, Hopper decides to take Deputy Powell along for a trip to the local library, where they delve into Hawkins Lab's murky past.
Their research uncovers startling revelations. Brenner has been involved in numerous shadowy government projects, delving into the supernatural. Moreover, a woman named Terry Ives once accused Brenner of stealing her daughter, adding a chilling layer to the already mysterious case. Deputy Powell remains skeptical, but Hopper is adamant that they must dig deeper.
Eleven experiences a flashback, revisiting a dark chapter of her past with Brenner, whom she calls "Papa." He punishes her severely for refusing to harm a cat with her telekinetic powers, locking her away in solitary confinement. But when, in a panic, she lashes out and accidentally kills two orderlies who are manhandling her, Brenner is strangely impressed.
Nancy's heart is heavy with worry over Barb's disappearance. Meanwhile, Steve and his friends discover that Jonathan has snapped photos of their house party, sparking a confrontation. They gang up on him, destroying the photos and his camera. But Nancy, sifting through the wreckage, spots a picture of Barb by the poolside, prompting her to return to Steve's house in search of clues.
There, Nancy finds Barb's abandoned car and glimpses the creature lurking in the woods. Back at her home, Joyce and Will establish a secret code using the Christmas lights. Through a series of flashes, Will manages to convey that he is alive but in danger. Suddenly, a creature begins to claw through her wall, and Will frantically tells her to flee.
Later, a shocking discovery is made. Will's apparent body is found floating in the water at a nearby quarry, leaving everyone reeling from the realization that the monster they are facing is more real and more dangerous than they ever imagined.
