Willis's mythos is a near future, first introduced in her story "Fire Watch" (1982), in which historians conduct field work by traveling into the past as observers.

[5] Kivrin Engle, a young historian specializing in medieval history, asks her reluctant instructor, Professor James Dunworthy, and the authorities running the project to send her to Oxford in 1320 near Christmas.

[5] Shortly after sending Kivrin to the 14th century, Badri Chaudhuri, the technician who set the time travel coordinates for the trip, collapses, an early victim of a deadly new influenza epidemic that disrupts the university and leads to the city being quarantined.

Kivrin discovers many inconsistencies in what she knows about the time: the Middle English she learned is different from the local dialect, her maps are useless, her clothing is too fine, and she is far too clean.

This causes the acting head of Balliol College Professor Gilchrist to order the net closed, effectively stranding Kivrin in the past.

Though there was no slippage (the time shift between a traveler's intended and actual date of arrival, ensuring they cannot change history), it is discovered that Badri, delirious with illness, input the incorrect coordinates.

Ahrens and Dunworthy discover Badri contracted the influenza virus from human remains at the archaeological dig, starting the epidemic at future Oxford.

Within days, many residents of the village fall ill, and Kivrin, who is vaccinated and immune, attempts to help Father Roche treat them.