In a world where animal cloning has skyrocketed in innovation since the famous duplication of Dolly the sheep, human cloning remains strictly illicit under the so-called "Sixth Day" laws, enforced after a grim incident surrounding the first cloning attempt.
Meet Adam Gibson, a charter pilot who becomes embroiled in a tangled conspiracy when he takes on a job from Michael Drucker, the secretive billionaire behind Replacement Technologies. During what he assumes is a routine drug test as part of their agreement, Adam's life spirals into unpredictability.
When tragedy strikes and his daughter's cherished pet dies, Adam seeks comfort by visiting one of Drucker's RePet cloning establishments. As fate would have it, his partner Hank masquerades as him and takes Drucker on a snowboarding trip, where tragically, he meets his end at the hands of Tripp, an assassin bent on revenge against Drucker.
Devastated, Adam opts for a life-sized animatronic doll instead of a clone, but upon his return home, he is shocked to find that a clone of himself has already been introduced into his family. Before he can react, Adam is forcibly taken by Marshall, Drucker's security chief, along with agents Talia and Wiley.
In a fight for survival, Adam escapes, dealing lethal blows to Talia and Wiley, yet he grapples with the confusion of his circumstances. Declared an escaped mental patient by the authorities, he is left with no choice but to go underground.
Meanwhile, Drucker survives his assassination attempt and reassures the media of his intention to uphold the Sixth Day laws. But behind closed doors, he and Dr. Griffin Weir, his chief scientist, have been clandestinely perfecting human cloning. Hidden from public view, they bring clones of Talia and Wiley back to life, setting the stage for a chaotic confrontation that challenges Adam’s understanding of his own identity.
As Adam maneuvers through this perilous environment, he must confront the ethical dilemmas surrounding cloning and Drucker's hidden agendas. With Hank's apparent demise, Adam questions if the clone is merely an echo of himself or something more valid. The boundary between reality and imitation gets increasingly nebulous, prompting Adam to reflect on the ramifications of humanity's desire to play God.
The tension escalates when Marshall and Talia intrude on Adam's life, forcing him to impersonate his clone to safeguard his family. This puts Adam in a moral quandary: should he eliminate his clone or allow it to exist? The ramifications of this decision could reverberate through both his family life and society as a whole.
In this whirlwind, Drucker is cloned again alongside Hank, complicating the intricate web surrounding Adam. As he navigates these convolutions, he also faces Tripp, who reveals his role as an anti-cloning radical manipulating events from the shadows to serve his agenda.
With everything turned on its head, Adam stands at a pivotal junction. Should he resist the growing cloning industry, or find a way to adapt to its consequences? This choice will undeniably impact Adam's self-perception and the future trajectory of human cloning.
In a shocking twist, Weir discloses to Adam that DNA scans and memory assessments of him resulted in the formation of a "syncording," a digital imprint for potential replication. The revelation becomes even more startling as Adam learns that Drucker had undergone cloning years earlier, a ploy to safeguard his riches since clones lack legal standing.
When both Adam and Hank are believed lost with Drucker, Weir resorts to cloning them to cover for Drucker's murder while obscuring the existence of his own clone. The stakes rise when Weir warns Adam that Drucker will likely pursue his clone with lethal intent.
In a desperate effort to shield his family, Adam agrees to hand over the incriminating syncording to Drucker for the safe return of his wife and daughter. However, this plan crumbles when Talia and Vincent abduct Clara and her daughter at a school event, substituting them with their own clones.
The drama builds as Adam confronts his own clone, spiraling into an existential dialogue. They forge an alliance, with Adam poised to deliver the syncording to Drucker for the safety of his loved ones. But their fragile truce shatters when Weir confronts Drucker, exposing his scheme to create multiple clones—including Katherine, Adam's wife—programmed with shortened lifespans to sidestep betrayal.
In a moment of violent climax, Drucker eliminates Weir, promising to resurrect both him and Katherine as clones. To counteract this, Adam deploys a decoy helicopter for destruction while stealthily landing on Drucker's helipad, determined to unleash chaos from within.
Captured by Drucker's operatives, Adam is revealed to be the clone, with his true identity confirmed by a unique mark inside his eyelid. Yet, the true Adam is already inside the facility, on a mission to save his family.
As the original Adam liberates his family, his clone fights bravely against Drucker's forces but ultimately falls victim. In a final rebellious act, a dying Drucker attempts cloning again, only for the malfunctioning equipment to produce a grotesque, imperfect version of himself.
Ultimately, Adam and his clone escape via helicopter, obliterating the facility and its syncordings as Drucker meets a fatal end.
In a bittersweet conclusion, the real Adam arranges for his clone to commence a fresh life in Argentina, overseeing a satellite office of their charter operation. The clone gifts Adam's family with Hank's cherished RePet cat, while they bid farewell to their doppelgänger with a heartfelt send-off.
