In the dystopian setting of 2067, Earth has suffered immensely due to climate change and relentless nuclear warfare. Among the desolation, a solitary city in Australia survives, relying on a toxic form of synthetic oxygen that leads to a deadly condition known as "The Sickness." At the heart of this bleak world is Ethan Whyte, portrayed by Kodi Smit-McPhee, a manual laborer burdened with the care of his wife, Xanthe (Sana'a Shaik), who is stricken by the illness.
One fateful day, Regina Jackson (Deborah Mailman), the Chief Technology Officer of Chronicorp, summons Ethan. She reveals the dire situation: the Sickness threatens to extinguish the last vestiges of humanity. During a demonstration of the "Chronical," a pioneering time machine developed by Richard Whyte (Aaron Glenane), Ethan's father who passed away two decades earlier, a radio transmission penetrates the timeline, specifically requesting Ethan's presence in the future. Initially resistant, fueled by resentment towards his father for leaving him and his mother, Ethan finds his resolve shaken by the urging of Xanthe and his guardian, Jude (Ryan Kwanten).
Upon traversing time, Ethan awakens in a vibrant rainforest, clutching only a hand-held device named Archie and a wrist gadget gifted to him by Richard in his youth. He stumbles upon a bunker, where a skeleton in his jumpsuit awaits—a chilling reminder of his fate. Overwhelmed with despair, Ethan discovers that he has become another ghost of his future. Just as he succumbs to poison berries, Jude emerges, having followed Ethan's declining life signals back through time to save him.
After sharing clues from this dystopian world's remnants, they decipher directions from Archie leading them to the lab of the Chronical. Here, Ethan learns that his wrist device is a DNA analyzer crafted for him to gain access to the Chronical's inner workings, which is set for a reactivation in a mere four hours.
They uncover a holographic message from Richard, detailing that the goal of the Chronical project was to revive an atmospheric monitoring facility to gauge Earth's viability for future habitation. However, a mishap revealed a startling directive: Richard was instructed to send Ethan to the future. Yet, a critical complication manifested—without an operational link from both timelines, sending living beings through time remained an insurmountable challenge.
As they move to activate the Chronical, it malfunctions, endangering their time and the existence of their world as it approaches a nuclear meltdown. The duo embarks on a perilous journey to the power core, navigating through ruins littered with remnants of humanity, including Xanthe's remains, a grim confirmation that a cure for the Sickness was never found.
In a moment of despair, Jude tries to console Ethan, but the recognition of Jude's voice from a tape found alongside Archie's remains reveals the heartbreaking truth of Ethan's future demise. Realizing Jude's intentions escalate to extremes, he forces Ethan to the reactor at gunpoint. In a desperate act, Ethan chooses to confront the reactor's core rather than remain a passive victim.
With time slipping away, Ethan discovers an exit that connects him to his skeleton, leading to a mental breakdown where he pleads for Jude to end his life, a request Jude passionately rebuffs. Confronting what he believes to be the truth, Ethan locks Jude away and listens to his father's last moments captured on tape. He understands that the mission was never built on hope; Regina Jackson aimed to escape to the future with a select few, discarding humanity's preservation. Risking everything to thwart Jackson's nefarious plans, Ethan learns that Richard keyed the time machine to his DNA to ensure its proper use.
In a dramatic climax, Ethan's revelation leads him to a confrontation with Jude, who, tormented by guilt, ultimately takes his own life. Before Regina can carry out her betrayal, Ethan sends a crucial message back to the past, along with a damning video of Richard’s murder, a collection of live plants, and a heartfelt goodbye to Xanthe. This act of defiance destroys the Chronical and irrevocably alters the timeline: in the past, Regina faces justice as the recording reaches the authorities, and the life-giving plants rejuvenate the planet.
In the newly redefined future, Ethan discovers his former city transformed into a flourishing utopia, harmonizing modern architecture with nature, yet eerily devoid of human life. The journey that began in despair culminates in the delicate balance of fate, where the remnants of hope linger amidst the ruins of what once was.
