Upgrade features an interesting sci-fi premise, so we break down everything about the movie’s shocking ending and what happened with STEM. Blumhouse’s Upgrade is set in the near-future and follows a mechanic named Grey Trace (Logan Marshall-Green), who is left paralyzed after an attack in which his wife, Asha (Melanie Vallejo), is killed. Devastated, Grey’s approached by tech genius Eron (Harrison Gilbertson), who offers to implant him with an experimental technology, a computer chip called STEM that restores his mobility.