Plot
Professor Edward Johnston leads an archaeological study of the village of Castlegard, near La Roque Castle in Dordogne, France, the site of the 1357 hanging of Lady Claire, sister to Arnaut de Cervole. Her martyrdom led France to win the Hundred Years War against the English. Johnston's team includes Scottish archaeologist André Marek; Johnston's students Kate Erickson, Josh Stern, and François Dontelle; and his son Chris. While excavating a nearby monastery, they find a sarcophagus containing the remains of a French knight with a lopped ear, holding the hand of his lady, an unheard-of practice for the time.
Johnston travels to the American headquarters of the ITC Corporation, his project's sponsor, to inquire whether or not they have tampered with the site. The students discover a lens from Johnston's bifocals and a note begging for help, although both date over 600 years old. When the students contact ITC, the company invites them to its headquarters.
There, the team is introduced to ITC president Robert Doniger and vice-president Steven Kramer. Doniger reveals that in the process of developing teleportation technology, they locked onto a stable wormhole to 1357 Castlegard. Johnston was invited to see the past for himself, but his group has not returned, and they want the students to go back in time to locate him. All but Josh volunteer to go.
The volunteers are stripped of all modern technology save for pendant-shaped markers they can use to initiate their return. The students are joined by a security team including ITC's head of security, Frank Gordon, and two former military men.
On arrival in 1357, the team finds itself in the path of a young woman chased by English knights; the security men are killed while protecting the group, although one activated his marker after priming a grenade. When his body arrives in the present, the grenade detonates and shatters much of the teleportation device. Josh aids Kramer in making repairs.
The team evades the knights, and the woman leads them to the English-controlled Castlegard. They are captured and brought before Lord Oliver de Vannes and his second in command, DeKere. The team members are stripped of their markers, and de Vannes kills François, believing he is a French spy. The others are imprisoned along with Johnston, who previously has promised de Vannes that he can make Greek fire for the English in exchange for his life. They make their escape but are pursued by the English. Gordon and Johnston are recaptured, while the others make for the monastery, led by the woman.
DeKere reveals himself to Gordon and Johnston as former ITC employee William Decker; he had frequently used the teleportation device but was not told by ITC that each use damaged his DNA until it was too late, at which point he would die on a return trip. He plans revenge on ITC and kills Gordon. De Vannes orders his knights to march on LaRoque castle, and DeKere brings Johnston along.
At the monastery, Marek, Kate, and Chris meet de Cervole and realize the woman is Lady Claire; they have changed history by saving her. Marek, who has become infatuated with Lady Claire, is given a horse to rescue his friends. Kate and Chris help to swing the upcoming battle in the French's favor by leading de Cervole's men through the monastery tunnels they had previously mapped to the castle.
As the battle starts, Marek is captured in his rescue attempt; Lady Claire is also kidnapped. Marek frees himself, Lady Claire, and Johnston, while Chris helps de Cervole defeat de Vannes. Enraged, DeKere slashes off Marek's earlobe, and Marek realizes he is destined to be the knight in the sarcophagus. Marek defeats DeKere, recovers the markers, gives them to the others, and says his goodbyes while running off to help the French assure victory and restore history.
As the three returnees activate their markers, in the present Josh and Kramer have finished the repairs after coming to learn that Doniger tried to sabotage their attempts; Doniger fears that when the students' stories become public, ITC will suffer great financial losses. As the machine activates, Doniger races into it, attempting to block the teleportation, but instead he is sent back to 1357, where he arrives outside the castle and is presumably killed by a charging knight.
Chris, Kate, and Johnston safely return. Later, the team returns to the Castlegard ruins, re-examine the sarcophagus, and find that Marek and Lady Claire led a prosperous life after the war and had three children: Christophe, Katherine, and François.
