Dustin nurtured the mysterious creature he stumbled upon in the garbage can with a 3 Musketeers chocolate bar, christening it d'Artagnan, or "Dart" for short. In a flashback, Hopper kindly left food in the woods for Eleven, who gradually overcame her wariness and drew closer to him. Hopper then escorted her to his grandfather's abandoned hunting cabin, assuring her that it was the safest haven for the moment.
In the present, Hopper steadfastly refused to let Eleven venture outdoors, insisting that it was still perilous. Frustrated by his caution, she sneaked out of the cabin during daylight and embarked on a quest to find Mike. Bob shared a childhood nightmare with Will, urging him to confront his fears head-on. Nancy persuaded Jonathan to accompany her in revealing the truth to Barb's parents, arranging a meeting with Barb's mother in a local park the following morning.
Hopper confronted Owens with compelling evidence that the blight originated from the lab. Owens, albeit reluctantly, agreed to investigate the matter further. Dustin eagerly brought Dart to school, introducing it to Will, Mike, Lucas, and Max. Will's eyes widened in recognition as he realized that Dart hailed from the Upside Down. As the group debated what to do with Dart, it suddenly molted and fled into the school, sparking a frantic search.
Meanwhile, Eleven happened upon Mike and Max as they were searching for Dart. From a distance, she watched them argue, mistakenly assuming it was flirting. Jealousy flared within her, and she caused Max to stumble off her skateboard. Joyce stumbled upon a chilling revelation while reviewing a videotape Will had recorded during a trick-or-treating adventure—an image of the monster lurking in the shadows.
Will's encounter with Dart triggered a haunting vision of the Upside Down. Dustin managed to retrieve Dart but kept its whereabouts a secret from the others. Following Bob's advice, Will braced himself to confront the monster, but it invaded his body, leaving him struggling to maintain control.
