Will is in the lab and loses much of his memory. The doctor claims the shadow monster is a virus and it's taking over Will. They realize that taking the tunnels down could kill Will. 

Nancy and Jonathan spend the night at Murray's and reaffirm that they are together after sleeping together. They return home and find Will's drawings. 

Dustin, Lucas, Max and Steve join forces and set a trap at the junkyard but they are shocked when more than one of the creatures show up. 

But, the creatures run off into the night and find themselves in the tunnel killing the laboratory workers. Will had led the men there thanks to the Demogorgon. 

The workers are all killed because Will lied that it's an area the monsters want to avoid.