The film introduces us to Courtney Holmes, portrayed by Elliot Page, as she embarks on a fateful journey with her younger sister, Tessa (played by Madison Brydges). In a tragic turn of events, Courtney gets distracted while driving and accidentally swerves off a bridge, resulting in Tessa's drowning. This traumatic incident haunts Courtney for nine years, during which she evolves into a dedicated medical student.
As she navigates her studies, encountering her colleagues Marlo (Nina Dobrev) and Ray (Diego Luna), Courtney finds herself amidst an unsettling experience while examining a patient, who questions her about loss. In pursuit of answers about the afterlife, she frequents the library where she meets Sophia (Kiersey Clemons), a fellow student overwhelmed by academic pressure from her mother. Their supportive camaraderie blossoms as they bond outside the library.
In a lecture by Dr. Barry Wolfson (Kiefer Sutherland), the students face his ire for their lack of preparedness. At lunch, Courtney invites her colleague Jamie (James Norton) to join her in a basement experiment that will push the boundaries of science and human experience. They aim to document what happens after death as Courtney decides to flatline her heart for sixty seconds while they monitor her brain activity—unbeknownst to the dangers that lie ahead.
While undergoing this harrowing experiment, Courtney has a surreal out-of-body experience that leads her to the hospital rooftop. However, Jamie and Sophia struggle to revive her afterward, sparking a frantic yet crucial intervention from Ray. The aftermath reveals a transformation in Courtney; scans show an enhanced hippocampus, suggesting her near-death experience has heightened her cognitive abilities.
The next day, armed with a recipe from her grandmother, Courtney impressively excels in Dr. Wolfson's class and showcases newfound musical talent, leaving her peers in awe. But amidst her achievements, she is haunted by visions, including her sister's presence, triggering fears and unresolved guilt from her past.
As the group delves deeper into their risky pursuits of flatlining, each friend faces their own demons. Jamie’s temptation leads him to flatline next, where he confronts unsettling memories with his ex-girlfriend Alicia (Anna Arden). Similarly, both Marlo and Sophia experience their personal confrontations with guilt and regret stemming from past actions.
With a thrilling convergence of events, the gang faces increasing peril as they push the limits of life and death. Courtney becomes increasingly disturbed by her visions, leading to a tragic climax where she falls to her death while being pursued by the ghosts of her past.
In the aftermath of Courtney's passing, her friends grapple with the burden of their collective guilt. They are pushed to confess their past wrongdoings, seeking redemption and reconciliation with those they have wronged. Each character’s journey reflects the overarching themes of regret, forgiveness, and the indelible shadows cast by their choices.
Ultimately, as they relinquish their reckless experimentation with death, they find solace in one another and pay tribute to Courtney’s memory—a poignant reminder of their lost friend. They gather to share a toast, reflecting on their painful journey while embracing the lesson of forgiveness and moving forward.
