Gregor edited the summary of Timeline Saturday, December 19, 2009.
The novel begins with a couple driving along a road in Arizona towards a near town when they are startled to see a man wandering in the middle of the road speaking deliriously and in need of medical attention. He is soon rushed to a nearby hospital where doctors notice veins, arteries and even bone joints misaligned in the man's body.
During this same time in a region in France, Professor Edward Johnston heads a team of historians and archaeologists studying a site in the Dordogne region of France where the medieval towns of Castelgard and La Roque stood. Suspicious of the detailed knowledge of the site shown by ITC (their funder), Johnston flies to ITC's headquarters in New Mexico to investigate. Soon the archaeologists begin to uncover modern objects in the ruins, recognizing among them the lens of Johnston's eyeglasses.
Researchers Chris Hughes, Kate Erickson, André Marek (a medieval enthusiast), and David Stern fly to ITC. Here they meet Robert Doniger, the founder of ITC. They learn that Johnston traveled back in time to the year 1357, to visit the site they were excavating, but has not returned as expected. Doniger insists that they travel back in order to retrieve Johnston. They are persuaded to do so and undergo the process of transferring their physical selves back to 1357. Accompanying them is a hardened marine and an experienced individual who works with ITC.
When they arrive in the past, the team is plagued by misfortune. They are attacked by a team of horsemen in pursuit of a boy suspected of being a thief, ultimately killing the ITC member and the marine. A grenade smuggled to the past by the marine is activated and sent to the present, destroying the transit pad and complicating the team's return. Kate and André see Johnston being taken away by the men of Lord Oliver of Castelgard.
Separated from the others, Chris follows the boy and accidentally declares himself as a noble. The boy leads Chris to Castelgard and is revealed to be Lady Claire in disguise, trying to escape from Sir Guy's clutches.
In the castle, Chris and André find themselves challenged to a joust by Sir Guy and his second (Sir Charles de Gaune). Chris, thanks to André's instruction, survives the joust and André defeats both Sir Guy and his second. Sir Oliver orders the death of André and Chris for dishonouring Sir Guy. Kate helps them escape, but from then on they are pursued by the forces of Oliver, most notably Sir Guy and Sir Robert de Kere.
Lord Oliver believes that Johnston knows a secret passageway into the otherwise impenetrable castle of La Roque. Arnaut de Cervole is approaching Castelgard to lay siege and Oliver must know this secret to successfully defend the castle. Johnston helps Oliver, despite knowing that, historically, he loses the siege, but he never gains Oliver's trust. Chris, André, and Kate use Johnston's clues (which they had uncovered in 1999) to find the secret passageway themselves in order to save Johnston.
Chris and company learn that someone else from 1999 is also in the past with them and has been spying on their transmissions, always staying one step ahead in their pursuit of Lord Oliver. It is revealed that Rob Deckard, an ITC employee and former marine, who went insane from an accumulation of "transcription errors" (slight errors that occur during the process of traveling that, over time, can physically and mentally alter the traveler), went back to 1357 more than a year ago and never returned. Eventually Robert de Kere reveals his true identity as Deckard to the researchers and tells them that he has no intention of permitting their return to 1999.
Kate, Chris, and André are captured by Arnaut's men but are saved by Lady Claire and later escape. André enters La Roque as Johnston's assistant. As Arnaut prepares his siege, Oliver decides that Johnston is hiding information and takes him to a torture device to drown him. Meanwhile Chris and Kate find the secret passageway and enter La Roque. Kate kills Sir Guy and Arnaut's men begin to enter La Roque. Arnaut and André find Oliver about to drown Johnston, but save Johnston and leave Oliver to drown instead. De Kere goes after Chris to get the marker beacon that will allow the travelers to go home, but Chris manages to kill him.
ITC and Stern finally repair the landing area just in time for the travelers to return. André—who had longed for the Middle Ages long before he knew that time travel was possible—decides to remain in the past with Lady Claire.
The group, including Kramer and Gordon, decide to send Doniger back into the past and leave him to die, as he was responsible for the mess. He presumably catches the Black Death.
Back in the present, Chris and Kate are together and expecting a child. The researchers find André and Lady Claire's graves, and discover that André lived a good life as a Medieval knight after they left him behind.