On a chaotic Mardi Gras day in New Orleans, a ferry carrying Navy sailors and their families across the Mississippi erupts in a devastating explosion, killing 543 people. Doug Carlin, Denzel Washington, an ATF Special Agent, discovers evidence of a bomb planted by a domestic terrorist and examines the body of Claire Kuchever, who appears to have died in the blast but is found alive in the river hours before the explosion. As he investigates, Doug learns that Claire had called the ATF office on the morning of the bombing, hinting that she was abducted and killed well before the catastrophe.
Impressed by his deductive abilities, Paul Pryzwarra, Val Kilmer, invites him to join a new governmental unit tasked with unraveling the crime. The team, led by Dr. Alexander Denny, Adam Goldberg, leverages a surveillance program called Snow White, a system the group claims can reconstruct events from roughly four and a quarter days in the past using past satellite footage to form a triangulated image. Convinced that Claire is a crucial link, Doug studies her past footage and manages to track the soon-to-be-bomber when he calls about a truck she has for sale.
Realizing that Snow White is more than just a record of the past, Doug persuades the team to attempt sending a note to his past self with the time and place the suspect will act. His partner, Larry Minuti, Matt Craven, finds the note but is fatally shot while trying to arrest the suspect. Using a mobile Snow White unit, Doug can follow the suspect’s past movements as he flees to a hideout with the wounded Minuti, and he witnesses Minuti’s murder in real time.
In the present, the bomber is identified as Carroll Oerstadt, Jim Caviezel, an unstable “patriot” rejected from military service. He confesses to killing Minuti and Claire, stealing her truck to transport the bomb, and staging her death among the ferry victims. The government closes the case, but Doug remains convinced that Snow White can alter history, so he convinces Dr. Denny to send him back to the morning of the bombing to save Claire and prevent the catastrophe.
Doug survives the time-shift and ends up in a hospital emergency room where doctors manage to revive him. He steals an ambulance and reaches the hideout in time to stop Claire’s murder, but Oerstadt shoots him and escapes with the bomb. Doug drives Claire to her apartment to tend to his wound, yet a wary Claire holds him at gunpoint and calls the ATF to verify his identity—the call his office received the day of the bombing. He manages to convince her of the truth, and they depart together for the ferry dock.
Doug boards the ferry, intent on disarming the bomb in Claire’s truck, but Oerstadt captures Claire and binds her to the truck’s steering wheel. A gunfight erupts, but Doug distracts Oerstadt with information drawn from his future interrogation, allowing Claire to ram him with the truck and enable Doug to shoot him dead. Doug climbs into the truck to free Claire, but police close in as time runs out. With no moment to defuse the device, they drive the vehicle into the river, saving the ferry passengers; Claire surfaces and swims free, while Doug is lost in the underwater explosion. rescued by a boat, a grieving Claire is later approached on the pier by the Doug Carlin from her present timeline, signaling a haunting reunion across time.
