Elite US Army Sniper Levi (Miles Teller) is retired and unwilling to take on any assignments but is persuaded by a shadowy Intelligence Operative (Sigourney Weaver) that the one she has for him is of suitable import.
He is shipped to "The Gorge" a giant mist-filled crevasse. He must crew the western watchtower and maintain the significant automated defensive perimeter, alone for a whole year. He's not there to keep people out but to keep what's inside from getting out.
His opposite number in the east watchtower, Drasa (Anya Taylor-Joy), is there to do the same on the behalf of Russia: this is some post-WWII Great Powers joint project that has survived the Cold War and the fall of the Soviet Union.
Communication across The Gorge is forbidden but as the months roll by boredom takes its toll and the pair start a weird long distance, drawn out flirtation.
No good will come of this.
CW: some body horror imagery