It's January 1985 -- the Hawkins crew have survived their battle with the mind flayer, but Will and Joyce are still reeling from the recent death of Bob Newby. After he and Mr. Clarke discover a mysterious map Bob left in a box of old nerdy memorabilia, Will rallies the crew to investigate -- but with a blizzard coming, they're afraid to follow. When Mike, Dustin, and Lucas learn that Will has taken off into the freezing wilds alone they rush to stop him. By the time they reach him, it's too late to turn back. They have no choice but to follow the clues further into a cave full of booby traps and mystery.