ATF Agent Doug Carlin (Denzel Washington) is investigating the terrorist bombing of a New Orleans ferry packed with sailors enjoying a break from work. The investigation deepens when the body of Claire Kuchever (Paula Patton) is found washed up near the explosion, but forensics suggests she was murdered many hours earlier. Following new leads he meets an FBI team led by Agent Paul Pryzwarra (Val Kilmer) who have a cutting-edge R&D think-tank project which allows them to glimpse 4 days into the past through 'satellite imagery' - although everything is not as it seems. Will he be able to change the past and save the girl?

Falling in love with Claire, Doug climbs into the machine and is warped 4 days into the past to save the day. He is revived in a hospital, and then slips out, steals an ambulance, and races to stop the terrorist (whose surname I could never spell) from setting fire to his hostage.
  He smashes the ambulance through the bad guy's house, takes a bullet, but rescues Claire. Back at her apartment he tries to tell her what has happened.

They get to the ferry, but the bad guy spies Claire's truck and hurries back on board. Claire follows him, but she is kidnapped by him, again, and chained to the steering wheel of the bomb-fitted truck.

There's a shootout. Doug gets into the truck and them ram, and kill, the bad guy. Ordered to get out by armed guards, instead they drive it off the ferry where it quickly sinks. Claire makes it out but Doug is trapped. The truck explodes, but most people on the ferry are safe.

Back on dry land, Claire is comforted and told an agent will be with her shortly - when she looks up she finds out that the agent will be none other than Agent Doug Carlin in this alternative reality. Getting into his car she is about to explain what has happened - but she may not need to as he seems to have a case of deja vu about it all anyway.