When Will Byers goes missing, his friends- Mike, Lucas, and Dustin- set out on a rescue mission but little do they know that their friend is no longer in this world, but in a parallel dimension called the Upside Down. On the other hand, a girl who is only known by the number Eleven escapes from Hawkins Laboratory. It is soon discovered this is no ordinary girl but she can move things with her mind. When Eleven meets Mike and his friends, they immediately bond and the rescue mission resumes. As the children delve deeper into the secret world of the Upside Down, they realize that this is just another version of their own world, only darker. The mystery soon begins to unfold itself giving terrible secrets about Hawkins Laboratory and the looming danger that has shrouded the town.