In 2054, on the icy planet Niflheim, Mickey Barnes (Robert Pattinson) serves as an "Expendable"—a clone engineered to perform deadly tasks for a colonization mission. After a mission gone awry, Mickey 17 is presumed dead and replaced by Mickey 18. However, when Mickey 17 returns alive, both clones must navigate their coexistence, challenging the colony's strict rules against duplicates. As tensions rise, they confront questions of identity, autonomy, and the ethics of expendability.