In Algiers, New Orleans, an unfortunate incident unfolds when a ferry, transporting sailors from the USS Nimitz along with their families during a Mardi Gras celebration, suffers a devastating explosion, resulting in 543 casualties. The lonely ATF agent Doug Carlin (Denzel Washington) is called to investigate this heinous act of terrorism. During his inquiry, he learns from Sheriff Reed (John McConnell) about the body of a woman named Claire Kuchever (Paula Patton), which has mysteriously washed ashore. Strikingly, her corpse, discovered an hour prior to the explosion, is burned and shares similarities with the blast's explosive residue. This revelation leads the team to suspect that her death was intricately orchestrated to appear as a part of the explosion, yet her body arrived prematurely.
As Doug delves deeper, he uncovers evidence that Agent Larry Minuti (Matt Craven), his partner, was also a victim of the bombing. He finds Claire's home and discovers a call was made to her earlier that day, most likely after her untimely death. Among the chilling finds are bloodstained rags, a firearm, and a cryptic message on her refrigerator that reads, “U can save her.” Claire’s SUV, presumed to be utilized in the explosion, is also missing, escalating the urgency of the investigation.
Doug’s quest leads him to a covert team headed by FBI Agent Pryzwarra (Val Kilmer), who introduces him to an experimental surveillance technology. This advanced system can resurrect visuals from just four days prior via an intricate satellite network. Pushing to find answers, Doug focuses on the enigmatic Claire Kuchever, discovering in her diary that she felt she was “being watched.” Soon after, she receives a menacing call from the terrorists regarding her vehicle, but they fail to meet for the transaction.
A surprising twist occurs when Doug interacts with the viewing system, leading the team to note Claire’s involuntary reaction, indicating that the images they observed were from the living. The scientists reveal notions of an Einstein-Rosen bridge and space folding technology. Despite assurances, they highlight the impossibility of sending living entities back in time, with even gerbils failing to survive the journey. Instead, they opt to send a message back to warn Doug of the impending danger.
However, their timing proves catastrophic, as the tip they send inadvertently leads Larry to his death during the confrontation with the terrorist. In a desperate race against time, Doug, anxious to save his partner and those impacted, launches a chase in a HumVee, trying to track down Larry before it’s too late.
Unfortunately, Larry's fate is sealed as he endures tragic circumstances at the hands of the terrorist Carroll Oerstadt (James Caviezel), who is later captured. Frustrated by the lack of preventive action, Doug visits Claire's home and recognizes the urgency written in the refrigerator magnets, which spell out a message of salvation. Upon gaining aid from Dr. Denny (Adam Goldberg), Doug resolutely volunteers to travel back in time to avert the calamity.
Re-emerging four days in the past within a hospital, Doug finds a way to rescue Claire from her impending doom. He crashes an ambulance into the building to confront Oerstadt and tries to fight for Claire’s life. In a tense climax aboard the bomb-ridden ferry, Doug and Claire engage in a desperate struggle against time and fate to thwart disaster.
After a series of heart-stopping confrontations and revelations, Doug courageously sacrifices himself to save Claire. As she makes it to the surface, mourning envelops her as the explosion consumes the depths below. Strikingly, moments later, aid arrives for Claire, revealing Doug, now from the present, approaching her with a bewildered sense of déjà vu. Their fateful connection re-emerges as he innocently echoes her poignant query: “What if you had to tell someone the most important thing in the world, but you knew they'd never believe you?” to which she response with, “I’d try.”
