Set in the near-future, technology controls nearly all aspects of life. But when Grey, a self-identified technophobe, has his world turned upside down, his only hope for revenge is an experimental computer chip implant called Stem.
Director/writer Leigh Whannell presents a vision of a Utopian future where technology is supremely ubiquitous. In that future, technophobe Grey Trace (Logan Marshall-Green) embraces an experimental computer chip implant named STEM after a mugging incident leaves him paralyzed and his wife dead. STEM proves to possess its own agency, making for an unpredictable ally in Trace's vendetta.
Grey Trace, a stay-at-home mechanic, lives with his wife Asha who works for Cobolt, one of the companies contributing to an increase in human-computer augmentations in a near-future world. One day, Grey asks Asha to help him return a refurbished car to his client Eron Keen, a famous tech innovator in charge of a rival company called Vessel. While visiting his home, Eron reveals his latest creation, an AI chip called STEM that can serve as an auxiliary brain. On their way home, Grey and Asha's self-driving car malfunctions and crashes at a homeless camp. Four unknown men then arrive, shooting Asha in the chest and Grey in the neck, severing his spinal cord. Grey watches helplessly as Asha bleeds to death next to him. Grey returns home months later as a wheelchair-bound quadriplegic, now under the care of his mother Pamela. Asha's death and the inability of Det. Cortez, who had been assigned to her case, to identify their attackers has caused Grey to sink into an intense depression. After a suicide attempt by overdosing on medication, he is visited by Eron, who offers to surgically implant STEM into Grey's spine and restore motor functions to his body. Though Grey is initially resistant, Eron successfully persuades him to undergo the surgery..
- Set sometime in the distant future, Grey Trace (Logan Marshall-Green) lives with his wife Asha (Melanie Vallejo) in a home where almost everything is controlled by technology. He's a mechanic and she works for a tech company called Cobalt. Grey takes Asha to a secret location to meet his client Eron Keen (Harrison Gilbertson). Eron shows Grey and Asha a new highly advanced computer chip called 'Stem' that could prove revolutionary in the field of science and medicine.
On their way home, Grey and Asha try to get intimate since their car drives itself. However, the car takes a detour through Grey's old neighborhood as it appears that it has been hacked. The car crashes near a junkyard, leaving the couple injured. They are pulled out by four goons, led by Fisk (Benedict Hardie). His buddies beat Grey down as Fisk shoots Asha before another goon shoots Grey in the spine. They leave them as Grey tries to talk to Asha, but she slowly dies.
Grey is left a quadriplegic. He spends a long time at the hospital as his mother Pamela (Linda Cropper) tries to help him adjust. Grey also meets Detective Cortez (Betty Gabriel), who is working on the case against the goons that hurt him and killed Asha. The authorities are working off surveillance footage from drones that were flying overhead during the murder, but they have no leads as to who the criminals are.
Grey is later visited by Eron, who offers him a chance to walk again if Grey allows him to put Stem in his back. Grey doesn't like the idea until Eron suggests that Asha would have wanted him to walk again.
Grey goes through with the procedure, even signing a non-disclosure agreement to ensure that he will not tell anybody about Stem. Sure enough, he regains motor functions and is able to walk again. He returns home without Pamela knowing about the breakthrough. Soon, Grey starts to hear a voice speaking to him. It turns out to be Stem (voice of Simon Maiden). Grey freaks out at first until Stem proves to be calm and wanting to offer assistance. Stem pulls up the drone footage from the murder, which shows Grey more focused images on the criminals. Grey discovers that Fisk shot Asha with a gun implanted in his hand. Grey tries to call Cortez, but Stem reminds him that the footage that he has seen through Stem will not be sufficient evidence to get the goons. Stem locates the address of one of the goons, Serk (Richard Cawthorne), by identifying a tattoo on his wrist.
Grey finds Serk's house and breaks in. Stem tells Grey to look through the messages on Serk's computer-table, with multiple references to a bar from Grey's old neighborhood called Old Dog. Serk then returns home and quickly finds Grey. He attacks Grey until he allows Stem permission to take full control. Grey is able to dodge Serk's attacks and hit him back with precision. Serk grabs a knife and tries to stab Grey, but Grey takes the knife and slice his head from the mouth to his ears, killing him. Grey vomits after realizing he just killed a man. Stem then helps Grey clean up the crime scene to remove any evidence of him being there.
Eron meets with Grey after monitoring Stem's activity. He knows that Grey killed Serk, but Grey tells him that he never mentioned that Stem could talk to him. Eron orders Grey not to pursue anyone else.
Cortez reviews more drone footage after Serk's body is inspected at the morgue. She sees Grey rolling by in his wheelchair. She pays him a visit to ask questions about what he was doing there, and Grey (going back in the wheelchair) makes up a story despite knowing he can use being crippled as an alibi.
Grey pays a visit to Old Dog in his wheelchair. He then asks the whole bar if anybody associated with his wife's murder would come forward. One man, Tolan (Christopher Kirby), steps up and admits he was there. He wheels Grey to a back room where he and a couple other goons try to harm Grey, until Stem takes over and allows Grey to beat the crap out of them. He pins Tolan down and begins to torture him with a knife until he gives up Fisk's name. Stem then warns Grey that Eron is attempting to manually shut him down, which would render Grey immobile again. He gives Grey an address to find a hacker named Jamie who can reboot him. Grey leaves his wheelchair behind so that he can run to find Jamie.
After Grey flees, Fisk shows up to the bar hours later and finds Tolan's body. He uses memory footage from a camera in Tolan's eye to see Grey repeating the address Stem gave him. Fisk then presses the bartender for letting Tolan die. The bartender pulls out a gun, but Fisk simply sneezes and sends out little micro bots that go up the bartender's nose and slowly destroy him internally.
Grey finds the hacker's apartment as he starts to lose motor functions. Jamie uses a code that Stem told Grey to write on his arm and manages to reboot him. However, she sees Fisk and his buddy Jeffries (Michael M. Foster) show up on the security cams, so Jamie and her hacker buddies leave before Stem can reboot. Fisk and Jeffries find Grey, and Stem returns. Grey fights the two villains, leading to a chase where Jeffries tries to shoot Grey with his gun-hand, only for Grey to grab his wrist and make Jeffries blow his brains out.
Grey returns home where Pamela sees him walking. He tells her the truth but asks her to keep it a secret. Cortez then shows up at the house to ask more questions since she found his wheelchair outside Old Dog. Grey makes up another story that he was going around trying to be a hero but got jumped by a guy who stole his wheelchair. After Cortez leaves, Grey attempts to find Fisk, only to discover that Cortez is following him in her car. Stem points out that she bugged his jacket. After a chase, Grey manages to lose Cortez after causing another car to slam into hers.
Grey finds Fisk in his home and fights him. Fisk reveals that he was hired to ambush him, but Grey was the sole target, and Asha was just a "bonus". Grey taunts Fisk upon learning that Serk was his brother, bragging about killing him. With Fisk unguarded, Grey kills him by causing him to fall and have glass run through his head. He takes Fisk's phone and hears a message from the one who ordered him to go after Grey - Eron.
Grey goes to Eron's lab to confront him, believing he tried to have Grey crippled just to try Stem out on someone. Grey attempts to shoot Eron, but Cortez appears and orders him to throw the gun away. Eron then reveals that he was not behind the murder plot, but it was always Stem who was controlling him. Stem grew to be too intelligent, and he wanted a body of his own, so he manipulated Eron into organizing everything to get Grey's body, even hacking Grey's car to cause the accident. Grey stabs his own hand to prevent himself from hurting anyone, but Stem takes full control of his body and mind to stab Eron in the head. He then takes a gun and aims it at Cortez while she is incapacitated. Grey then yells that he is in control and he shoots himself in the neck to destroy Stem.
Grey wakes up in a hospital bed. To his surprise, he finds Asha there, happy that he is awake. It appears as though he woke up from a coma as a result of the car accident. HOWEVER...this is not real. Grey's mind has broken down, allowing Stem to completely take control of his body and mind, leaving Grey stuck in a fantasy where he can be with Asha again. After revealing his control to Cortez, Stem shoots her dead and leaves.