I love these kinds of movies..

U.S. Army pilot Captain Colter Stevens wakes up on a Metra[6] commuter train going into Chicago. Stevens is disoriented, as his last memory was of flying a mission in Afghanistan. However, to the world around him – including his friend Christina Warren and his reflection in the train's windows and mirrors – he appears to be a different man: a school teacher named Sean Fentress. As he expresses his confusion to Christina, the train explodes whilst ing by another train, killing everyone aboard.

Stevens abruptly awakens inside of a dimly lit cockpit. Communicating through a video screen, Air Force Captain Colleen Goodwin verifies Stevens' identity and tells him of his mission to find the train bomber before sending him back to the moment he awoke on the train. Believing he is being tested in a simulation, Stevens finds the bomb in a vent inside the lavatory, but is unable to identify the bomber, trying to defuse it before the train explodes again.

Stevens again reawakens in his capsule and after demanding to be briefed, learns that the train explosion actually happened and that it was merely the first attack of a suspected series. He is sent back yet again, eight minutes before the explosion, to identify the bomber. This time, he disembarks the train (with Christina) to follow a suspect. This turns out to be a dead-end, the train still explodes in the distance, and Stevens is killed by a ing train after falling onto the tracks whilst interrogating a suspect.

The capsule power supply malfunctions as Stevens reawakens. He claims to have saved Christina, but Dr. Rutledge tells him that she was saved only inside the "Source Code". Rutledge explains that the Source Code is an experimental machine that reconstructs the past using the dead engers' residual collective memories of eight minutes before their deaths. Therefore, the only thing that matters is finding the bomber to prevent the coming second attack in Chicago.

On his next run-in, Stevens learns that he was reported as killed in action two months ago. He confronts Goodwin, who reveals that he is missing most of his body and is on life and hooked up to neural sensors. The capsule and his healthy body are "manifestations" made by his mind to make sense of the environment. Stevens is angry at this forced imprisonment. Rutledge offers to terminate Stevens after the mission, and Stevens eventually accepts.

After numerous attempts, including being arrested by the train security for trying to obtain a weapon, Stevens identifies the bomber through a fallen wallet, a nihilistic domestic terrorist named Derek Frost. Stevens memorizes Frost's license and vehicle registration plates. He discovers a dirty bomb built inside a van owned by Frost, as Christina follows him and both are shot dead by Frost. Outside Source Code, he relays his knowledge to Goodwin, which helps the police arrest Frost and prevents the second attack. Stevens is congratulated for completing his mission. Rutledge secretly reneges on his deal to let Stevens die, as he is still the only candidate who can enter Source Code.

Being more sympathetic to his plight, Goodwin sends Stevens back one last time and promises to disconnect his life after eight minutes. This time, he sets a date with Christina, defuses the bomb, apprehends Frost, and reports him to the police. He calls his father under the guise of a fellow soldier and reconciles with him, and sends Goodwin an email. After eight minutes, Goodwin terminates Stevens' life .

As the world around him continues to progress beyond eight minutes, Stevens confirms his suspicion that Source Code is not merely a simulation, but rather a machine that allows him to create alternate timelines. Christina and he leave the train and go on a date. In the same (alternate) reality, Goodwin receives Stevens' message. He tells her of Source Code's true capability and asks her to help the alternate-reality version of him.