In the year 2048, Earth finds itself in a dire state, plagued by overpopulation and violent conflicts that seem never-ending. In a race against time, a group of determined scientists, led by the esteemed Professor Martin Collingwood (Tom Wilkinson), seeks a new sanctuary for humanity on Titan, one of Saturn's moons. Among those chosen for a groundbreaking experiment is the skilled war pilot Rick Janssen (Sam Worthington), a man whose incredible ability to survive harsh conditions—including a harrowing three days in the Syrian desert without any nourishment—marks him as an unparalleled candidate for this ambitious mission.
As the experiment commences, the initial results appear promising. Rick demonstrates remarkable abilities; he swims with astonishing speed and remains submerged for almost forty minutes at a time. However, the euphoria quickly gives way to mounting concern as his wife, Abigail Janssen (Taylor Schilling), begins to notice alarming physical changes in him. While swimming together, she observes his veins darkening, a sign of the uncharted effects of the mutation process that he is undergoing as part of the experiment.
In a series of distressing events, the experiment grows increasingly intense, exposing Rick and his fellow subjects to conditions mimicking the extreme cold of Titan. After a grueling swimming drill, Rick finds clumps of hair falling out; another participant succumbs to a violent convulsion, dying tragically in the bathroom. Tensions rise further during a meeting when Zane, another subject grappling with mental strain, lashes out violently, revealing the psychological toll the experiment is taking on them all.
With growing unease, Abigail conducts her own investigation. She takes blood samples from Rick's vomit—noticing its darkening hue—while also discovering hidden cameras in their home. As Rick's condition deteriorates, resulting in a medical emergency and subsequent surgeries to adapt to the conditions of Titan, Abigail confronts Professor Martin about the ethical implications surrounding these manipulations. To her dismay, she finds he is just as uninformed about the consequences of the transformations her husband is undergoing.
The horror escalates when Zane, losing grip on reality, tragically kills his wife in a fit of rage before being shot dead by military personnel. In her desperation, Abigail steals a key card from the medical facility where Rick is being treated, leading her to unwelcome revelations about the gruesome fate of previous experiment subjects—autopsies revealing that they are merging human DNA with that of animals to create a new race, dubbed Homo Titanians.
Rick's transformation reaches shocking heights as he becomes progressively paler, experiences bleeding from his eyes, and eventually has to undergo significant surgical changes to prepare for life on Titan. When he finishes the transformation alongside a fellow subject, Tally Rutherford (Nathalie Emmanuel), the once beloved husband emerged as a stranger. Rick can no longer communicate with Abigail; his new form allows only for low-frequency sounds beyond the range of normal human hearing.
As the time for launch to Titan looms, turmoil erupts. Tally, now a fellow Homo Titanian, kills her husband and confronts Rick in an unsettling atmosphere where SWAT teams move in to contain them. Abigail, striving to protect her son, finds herself caught in a web of chaos. In an intense confrontation, Rick, realizing the monster he has become, flees from the military's pursuit.
Facing critical repercussions from the acclimation process to Earth's atmosphere, Rick is treated harshly by the authorities. Abigail, forced to intervene to save her husband, manages to switch out the dangerous solution intended to erase his memories with a harmless saline substitute. As Rick regains consciousness, he unleashes his newfound abilities in a violent episode against the military.
In an unexpected twist, Abigail, along with Dr. Freya Upton (Agyness Deyn), becomes embroiled in the conflict against Professor Martin’s authority. The colonel, swayed by moral qualms regarding the experimentations, decides to turn against Professor Martin and his orders. In a triumphant twist, they succeed in escaping, leading to their eventual transportation to the Titan II facility.
Ultimately, while Abigail assumes the pivotal role of head researcher, Rick is sent off to explore the mysteries of Titan alone. The film concludes on a poignant note, with Abigail gazing up at the stars, holding her son close, as they reflect on the uncertain fate that awaits their family, while Rick embarks on his solitary journey into the cosmos.
