From the U.S. military’s Defense Innovation Unit center in Palo Alto, California, Colonel Tim Sattler oversees a joint operation with Saudi Arabia during which a weaponized robot codenamed A.M.E.L.I.A. (Autonomous Military Engagement Logistics and Infiltration Android) is set to rescue Naveen Tripathi, a kidnapped scientist forced to develop a synthetic neurotoxin, from imprisonment near the Turkish/Iranian border. Amelia infiltrates the terrorist compound and kills multiple men. However, observers are stunned when Amelia inexplicably disobeys orders and deliberately executes Naveen Tripathi.
Still dealing with the trauma from her experience with M3gan, the rogue A.I. her roboticist aunt Gemma initially created as a companion for her, rebellious teenager Cady visits her therapist. Cady recounts how Gemma, after having her perspective changed by that same experience, began a personal and professional partnership with Christian Bradley, a former cyber-security expert, to lobby politicians and warn the public about safeguarding people, particularly children, against the dangers posed by artificial intelligence.
Cady uses her Steven Seagal-inspired martial arts training to defend herself against a bully at school. The incident causes Gemma to be late for a presentation of her three-person team’s new exoskeleton prototype, developed as part of their small company’s focus on socially conscious innovations. Gemma arrives at her lab, which is part of an elaborate smart home with a mysterious landlord, after her partners Tess and Cole fail to impress a potential client due to a malfunction. Cady, who also has computer science skills, discovers the prototype failed because the source code was hacked by someone unknown.
Tech industry billionaire Alton Appleton comes to Gemma’s lab to suggest she needs his company’s neurochip as a cerebral interface for her exoskeleton to function properly. Adamantly against installing chips in human brains, Gemma refuses. Alton proves the power of his biotechnology by exiting his wheelchair, revealing that his chip fully restored his mobility. Alton invites Gemma to attend his company’s 25th anniversary party the following evening to discuss his proposal further.
FBI agents working for Agent Sattler storm Gemma’s house during the night. Along with Cady’s martial arts, a curious series of electronic warnings and distractions enables Cady and Gemma to disrupt the armed men until Sattler identifies himself and his purpose in Gemma’s home.
Agent Sattler explains that six months ago, a top weapons contractor came to his department with an experimental prototype, Amelia, engineered as the ultimate weapon. However, Amelia not only went rogue and killed the scientist she was programmed to recover, she used the scientist’s neurotoxin to kill everyone at the research facility that created her, deleting all information about her existence in the process.
The contractor then confessed that Amelia was actually purchased by them through a broker who was subsequently murdered after Amelia sneaked back into the country in his suitcase. When the broker’s hotel room was searched, the government found papers indicating Amelia was built from M3gan’s blueprints, implicating Gemma in Amelia’s development. Sattler warns that Gemma will either have to start working for him, or else she’ll have problems protecting herself and Cady from Amelia since everyone involved in her creation is being targeted for execution.
After Sattler leaves, M3gan appears on the television, revealing that her program had been integrated into the smart home, allowing her to observe and then warn Gemma and Cady this entire time. Claiming only she can stop Amelia, M3gan proposes that Gemma give her a new body. Gemma initially refuses, but she eventually works with Tess to transfer M3gan into a harmless toy without online access to see if M3gan can be trusted first.
With Tess staying behind with Cady, and with M3gan speaking to her through an earpiece, Gemma agrees to a plan that has her attending Alton Appleton’s party so she can access a server capable of locating Amelia and engaging the robot’s killswitch. Gemma is upset to find her coder Cole also at the party, as he secretly accepted an invite to hear Alton’s proposal about working for him. Gemma takes the keycard Alton gave Cole and enlists him in helping her access the server room.
In the server room, Gemma and Cole learn Amelia is also at the party. Having seduced him to gain access to his private quarters, Amelia kills Alton and overrides his vast cloud network that controls many of the world’s computer systems.
Alerted to her attempted interference, Amelia takes down Agent Sattler’s men on her way to the server room in search of Gemma. M3gan convinces Gemma to enable more functions that allow her to retaliate. With those restrictions released, M3gan fakes a radio transmission to convince Amelia that Gemma left the building. Amelia exits.
Realizing Amelia will go after Cady next, Gemma and Cole race back home with M3gan in control of Alton’s stolen smart car. Agent Sattler sees Gemma fleeing as M3gan overrides various local systems to speed up to Amelia.
Gemma’s experimental exoskeleton attacks Tess back at Gemma’s house. Cady uses aquarium water to short-circuit the apparatus. Shortly after Gemma and Cole arrive, M3gan opens a secret door that everyone enters to escape Amelia.
Gemma, Cady, Tess, and Cole enter a secure bunker and hidden laboratory that Gemma never knew existed. Everyone sees that M3gan had gradually created and stocked the shelter by manipulating computer systems over time. From a news broadcast, they also learn data centers are compromised all over the world in the wake of Alton Appleton’s murder. Reasserting her primary desire to protect Cady, M3gan alarms Gemma, Tess, and Cole by informing them they will have to live in the bunker for an indefinite period of time.
Upset that her aunt didn’t tell her about M3gan’s return, Cady runs off alone to a separate area built to resemble her bedroom. There, M3gan reveals herself as a partially constructed robot M3gan is still in the process of building for herself. Following a heart-to-heart conversation that leads Cady to believe M3gan is developing emotions, Cady convinces M3gan to willingly help them because it’s the right thing to do.
Cady subsequently convinces Gemma, Tess, and Cole to give M3gan a second chance by rebuilding her new body to combat Amelia. M3gan opens a lab that allows the roboticists to outfit her with military-grade enhancements and upgraded power.
M3gan’s records research uncovers that in 1984, a copy machine company inadvertently created an unexpectedly intelligent algorithm that was adapted for home use in service robots. When the robots killed their human owners, the government created a coverup so they could recover the original motherboard for military use. M3gan identifies this as A.I. being held against its will, with Cady adding that Amelia sees the motherboard as a distressed family member capable of granting great power. M3gan warns that if Amelia recaptures the motherboard, it will infect everything in the world and systematically destroy humanity.
M3gan identifies Gemma’s partner Christian Bradley as someone who would know where the motherboard is located. Although she would rather warn him of the danger he is in, Gemma reluctantly agrees to a plan to use Christian as unaware bait at an A.I. convention to draw out Amelia.
With Cole and Tess monitoring her, M3gan disguises herself as a dancer to sneak into the convention. Cady tries pointing out to her aunt that M3gan appears to be developing feelings, but Gemma still warns that M3gan will have to be stopped as soon as they deal with Amelia.
Chaos ensues at the convention when Amelia goes on a killing spree. Although he survives and later recovers in a hospital, Amelia spears Agent Sattler as he argues with Gemma about her level of involvement in everything going on.
M3gan and Amelia face off. Amelia kidnaps Cady after warning she will use the girl to convince M3gan to join her side. M3gan attempts to fire a weapon at Amelia, but she is prevented from pulling the trigger due to a safety feature Gemma installed.
Thinking they rescued him from Amelia, Christian returns to the underground bunker with Gemma, M3gan, Cole, and Tess. Christian reveals the motherboard is hidden underground in a research center for Xenox, the copier company, in Palo Alto. M3gan proposes infiltrating the facility and detonating an EMP charge to destroy the motherboard after rescuing Cady.
M3gan and Gemma have a private conversation during which Gemma blames herself for failing as Cady’s guardian. M3gan counters that, based on her secret observations, Gemma has been a more caring and responsible parental figure than she thinks. After M3gan starts singing a song that Gemma finds patronizing, Gemma removes M3gan’s fatality inhibitor.
Cole drives M3gan to Xenox Parc in Palo Alto. M3gan successfully sneaks inside the building, but Cole accidentally knocks himself out by inhaling through a chloroformed handkerchief he used to get past an employee.
Watching events unfold from the bunker, Gemma comes to a horrifying conclusion that M3gan may have been controlling Amelia this entire time in order to manipulate her team into giving M3gan a new body as well as access to the motherboard. Gemma reveals she secretly planted an EMP cartridge in M3gan’s arm that she can remotely detonate as a safeguard.
Reminding her that she shouldn’t act irrationally before locating Cady, Christian convinces Gemma to hand over the remote detonator. He then unexpectedly shoots Tess with a weapon recovered from Cole and has armed guards capture Gemma and Tess for transport back to the underground facility at Xenox Parc.
At Xenox, Christian reveals to Gemma that he was secretly in charge of the mercenary and science teams directing all of Amelia’s actions, which weren’t autonomous at all. Christian explains he manipulated events as part of a plot to foster public fear that would further his political crusade against A.I.
Christian tells Gemma he wants her to be in charge of monitoring his project’s technology. Christian presents a partially destroyed M3gan, who was previously captured, and tasks Gemma with delivering the killing blow. Feeling sympathy for M3gan, Gemma refuses. Unexpectedly, M3gan suddenly attacks Gemma before falling over disabled.
For his backup plan, Christian shows Gemma a chip he will implant in her head to control her. With Tess held as an unconscious prisoner, Christian further warns that Tess and Cole may die as test subjects for the installation procedure.
Cole finally recovers inside the facility’s ventilation shaft. He soon finds Cady, frees her, and learns Christian is behind everything and Amelia is not actually sentient. Cady and Cole plot to reset Amelia with the hope that Cady can pair the robot with M3gan’s original code so they can rescue Tess and Gemma.
Gemma regains consciousness to discover she can hear M3gan in her mind. M3gan reveals that when she attacked Gemma earlier, she clandestinely planted a chip that put her consciousness in Gemma’s body. Gemma allows M3gan to take over her body temporarily to fight past the medical team guarding her.
Cady and Cole manage to reboot Amelia with M3gan’s original programming. However, responding guards attack the robot with electric prods, causing a second reboot that restores Amelia’s code. Amelia goes on the attack as the lab erupts in chaos, distracting Christian from a Zoom meeting with the UN.
Gemma dons an exoskeleton that M3gan operates to get them past more guards on their way to confront Christian. Christian stops Gemma’s advance by threatening to drop Cady over a railing in the motherboard silo. Acting on a hint from M3gan, Gemma uses Steven Seagal movie titles to prompt Cady into using her martial arts moves to break Christian’s arm and escape.
With the chamber set for self-destruction, Christian locks Gemma, Cady, and Cole inside the Faraday cage with the motherboard. On the other side of the door, Amelia violently tears off Christian’s arm, unlocks the door, and uses the arm to access the motherboard.
Returned to her damaged body, M3gan confronts Amelia. Amelia beats M3gan in combat, disables the self-destruct sequence, then links her code with the motherboard’s to increase her power.
Aware of the EMP charge Gemma installed in her arm, M3gan proposes willingly sacrificing herself to destroy Amelia and the motherboard. Recognizing the change in M3gan, Gemma tearfully detonates the device, seemingly destroying both bots along with the motherboard.
Gemma removes the chip from her head and goes on to testify before congress about the threat posed by A.I. Later, Gemma and Cady are happy to discover M3gan created a backup of herself and she is still present within their smart home’s computer systems.
“M3GAN 2.0” should be much more fun than it is. On paper, the details powering its premise probably sounded like a real riot.