Jim accidentally fell into a mysterious tunnel hidden beneath the ground.This tunnel is filled with a strange atmosphere, with unknown floating objects scattered everywhere, and vibrant vines growing around it.At the same time, his friend Will also fell into an unknown danger.Will feels himself resonate with a creature called the shadow monster, and he can feel its pain, discomfort and bloodthirsty nature.

After Mike learned of Will's experience, he came to visit.He comforted Will, thinking that his current state was like a spy, and he could sense things through the shadow monster that ordinary people could not detect.Dustin, on the other hand, realizes that his pet Dada has turned into a dangerous monster and he has to take steps to trap it.Dustin manages to lure Dada into the underground utility room after his mother leaves home, but he is confused about what to do with the monster and turns to his friends for help.However, everyone was busy with their own affairs and no one responded to his request, so Dustin had to turn to Steve for help.

At the same time, Eleven sensed that her mother was still alive through her superpower and found her residence.There, she saw her and her mother's past and learned that her original name was Jane.But when she saw her mother again, she found that her mother had gone crazy and kept chanting some strange words: “rainbow, sunflower, turn left three times, turn right four times...”

Nancy and Jonathan decided to continue searching for the truth, so they found a strange phenomenon researcher, hoping to get clues from him about Barbara's whereabouts.Although the short time together did not lead to any major discoveries, the relationship between the two developed by leaps and bounds during this period.When a new day comes, they kiss passionately as soon as they meet.

Jim's disappearance worries Joyce.Will drew many pictures of vines based on his feelings. After joining these pictures together, Joyce found that they formed a huge vein diagram.Mike combines Jim's disappearance with Will's description and marks a point on the map, thinking Jim might be there.

At this time, Bob accidentally visited Joyce.Although he was full of doubts, under Joyce's order, he had to suppress his curiosity and observe the pictures carefully.Suddenly, he spots familiar shapes and deduces that the vines are actually a map depicting the town's underground tunnels.Joyce, Mike and Will immediately set off to the location marked on the map in hopes of rescuing Jim.

They finally found Jim entangled in vines in the cave, and after some efforts, they finally freed him.However, just as they were about to leave, a group of lab personnel wearing hazmat suits appeared and took them back to the surface.Just when Joyce thought it was over, Will suddenly fell to the ground and began twitching and screaming.It turned out that the laboratory personnel were burning the vines with fire, and Will felt the pain of the vines.