CBR

Chief Hopper's letter to Eleven could be crucial to Stranger Things Season 4. 1 / 8

Hopper is assumed dead after the Russian reactor exploded in Hawkins. 2 / 8

However, his old letter asked Eleven to keep the door open three inches. 3 / 8

That was his way of monitoring her and Mike in her bedroom. 4 / 8

Fans, however, think it foreshadows he's alive and trapped in the Upside Down. 5 / 8

Theorists believe Eleven will have to crack the rift open to retrieve him. 6 / 8

This might even take them to Russia, where 'an American' is being held. 7 / 8

Thus, Eleven would need her powers back and allies for a search and rescue mission. 8 / 8