It's Christmas Day 1984.
Everyone is happy, everyone is safe.
Eleven goes outside for some fresh air, and then doesn't come back again.
On Boxing Day, she's found half frozen to death by the quarry... only that's not all. El doesn't remember anything. Not her name, her family, anything. She doesn't even remember that she has powers. And it's up to Mike and the others to make the painful decision... do they try and get their old El back? Or do they leave her to continue living as she is, a totally different person, but also oblivious to any of the horrors that she has been through in the past?
But when Will starts to sense that the Upsidedown isn't quite as dead as they all hoped it was, and a mysterious young woman with an 008 tattoo suddenly arrives, claiming that she was at the lab with Eleven when they were children and that she can sense something is seriously wrong, it's clear that they're all going to have to work together to try and reach the old Eleven before it's too late... but that task alone might prove harder and more dangerous than anything they've taken on before...