Paul Walker, Frances O'Connor & Gerard Butler
In present-day France archaeologist/professor Edward Johnston and his students are excavating a site near the ruins of Castlegard. The village had been burned in 1357 when a massive battle occurred at nearby La Roque Castle, during The Hundred Years War. Even though the English were strong, the French were able to defeat them. Lady Claire, the sister of Arnaut de Cervole was hanged by the English at the castle in full view of the French. This enraged the French so much that they won the battle against the English.
Johnston and his students Kate Erickson and Andre Marek live for the past. Johnston's son Chris does not share this passion but he visits his father from time to time mainly to be with Kate, on whom he has a crush. At one point while showing him a sarcophagus of a man and woman who have their hands folded into each other, Marek tries to explain to Chris that our future lies in the past. They notice that the man sculpted on the sarcophagus has no right ear: it was crafted that way.
While the professor is away reporting to his U.S. sponsors, ITC, Marek and Kate discover an old parchment along with a present-day bifocal lens. Examination shows the writing on the document pleading for help is from the professor, but it was written on April 4, 1357. Confused, Chris calls his father, but he's told his father is no longer there. ITC does, however, invite Chris and the students to its base in New Mexico.
There, they learn time travel is possible and Johnston is now trapped in 1357 near Castlegard, exactly the spot of the excavations. Since the students are the closest thing to experts on the location and the time period, they are asked to go back in time and rescue Johnston. With the exception of team physicist, Josh Stern, they agree and are joined by security man Frank Gordon and military personnel Jimmy Gomez and Bill Baretto. They are given several markers that, at the push of the button, will bring them back home, and are told if they aren't back in six hours, they might not be able to return at all.
They arrive in a rushing river. Once on land, they find themselves in the middle of a battle between the English and the French, and Gomez is quickly beheaded and Baretto, just as he is about to throw a grenade, is struck with arrows and uses his marker to return to the present. Marek is caught up in the battle and saves the Lady Claire by slaying a knight who was attacking her. She brings Marek to the safety of her village, but they're overheard talking to her brother Arnaut by an English spy and captured by the English.
They're seen as spies and are brought before the English Lord Oliver de Vannes, who kills one of the students, Frenchman Francois Dontelle.
The group is reunited in prison with Johnston and devises an escape plan based on their knowledge of the day's events. Unfortunately, they don't take into account that their presence has already changed the timeline.
Meanwhile in the present day, Baretto returns to the laboratory and dies, the grenade in his hand exploding and severely damaging the machines. Stern, ITC president Robert Doniger
, and vice-president Steven Kramer work as hard as they can to fix them, but Doniger
prepares to write the students off as "lost".
The time travelers are forced to remain involved in the battle and are able to change history by saving Lady Claire's life. At the same time, they learn of the presence of former ITC employee William Decker, who has stayed in the past (and is now known Lord DeKere) because damage to his internal organs indicates another jump will kill him. This flaw, which damages internal organs, in time travel was withheld from them by Doniger
Decker kills Gordon and steals all but one of the markers, forcing the professor and Marek to fight against the French, while Chris and Kate fight with the French against him and Oliver's English forces. At a church near Castle La Roque, the pair discover a tunnel leading into La Roque and tell Lord Arnaut, the French commander, of the tunnel. Arnaut and Chris fight their way through English forces. Chris, caught by Lord Oliver, is saved by Arnaut and quickly rushes to join Kate. They - Chris, Johnston, and Kate can return home. Marek, who has discovered his destiny, gives Chris the last marker and remains behind with his newfound love, Lady Claire. Doniger
tries to stop them returning but Stern rushes to stop him and he gets trapped in the machine. As the students and the professor return Doniger
is sent back and killed by an approaching knight.
Back in present-day France Kate finishes the dig on a sarcophagus by the old Castle La Roque. She and Chris are now dating as well. The inscription revealed on the sarcophagus is of Marek and Lady Claire, whose three children were named Christopher, Katherine, and François. Marek tells his surviving friends he chose a wonderful life, although he lived only twenty-five years longer in the harsh medieval world.