Marek find Johnston at a monastery, but he is soon taken captive by the soldiers of Lord Oliver de Vannes, an English knight and resident lord of Castelgard, who is convinced Johnston knows the secret passageway to the otherwise impregnable castle of La Roque, which Oliver controls. Oliver's enemy, French commander Arnaut de Cervole, plans to attack Oliver's domain, and Oliver wants the secret to defend it. Separated from the others, Chris follows the boy and inadvertently identifies himself as a nobleman. The "boy" leads Chris to the castle of Castelgard, and is revealed to be Lady Claire d'Eltham in disguise. She is being pressured to marry Sir Guy de Malegant. Chris and Marek (who has since found Chris) are challenged to a joust by Guy: Chris's apparent nobility and him accompanying Lady Claire have turned him into the enemy of Guy. The two survive the challenge thanks to Marek's knowledge of medieval combat. Oliver orders the historians' imprisonment. They escape Castelgard and are pursued by Sir Robert de Kere, Oliver's advisor. Meanwhile, Oliver relocates to La Roque, taking Johnston with him. In order to rescue Johnston, the historians search for clues to the location of the secret passage to La Roque. After gathering information at the monastery, they find a clue in a water mill, but get captured and interrogated by Arnaut. After escaping Arnaut's forces, Chris and Kate find the entrance to the passage at a decrepit chapel while Marek gains entry into La Roque by posing as Johnston's assistant. Marek learns that the professor is helping Oliver build an incendiary weapon to use against Arnaut's forces, believing that Oliver will lose the siege anyway as he historically does. The historians have learned that another person from the present is helping Oliver's forces. The person is revealed to be de Kere, who is really Rob Deckard, an ITC employee driven insane from errors in the process of teleporting to another time that built up in his body over multiple trips, much like the elderly man the couple in Arizona found. Deckard plans to prevent the historians' return to the present and kill them. Chris and Kate use the passage to enter La Roque. Arnaut begins the siege of La Roque, and later enters the castle by apparently using the passage. During the battle, Kate is chased by Guy and sends him falling to his death. Marek and Chris