The mysterious Tristan Lyons hires Dr. Melisande Stokes, a Harvard linguistics lecturer, to translate a variety of historic texts.

Stokes and Lyons discover that photography nullifies magic in the general area by causing a wave function collapse.

Lyons recruits Dr. Frank Oda, a former MIT physicist who once worked on a device that could prevent wave function collapse.

stands for the Department of Diachronic Operations, and that Lyons intends to build a device that will enable magic-assisted time travel.

Agents are trained in period-specific languages and combat techniques and magically sent back to 1601 London and the 1203-1204 Constantinople, among other times and places.

The object is to alter historical events to subtly help the United States government, but it has to be done carefully and methodically to avoid Diachronic Shear, a catastrophic magical explosion that occurs when history is changed too much or too quickly.

[2][3] Kirkus Reviews wrote that the "story gets weirder and more madcap" as it goes, but called the novel "a pleasing combination of much appeal to fans of speculative fiction.