There Will Be Time.
See:
Havig Versus Wallis and Havig Versus Wallis II, both here. (Scroll down.)
We, editorially speaking, find that we have already summarized this part of the novel in more detail than we would have thought possible! No need to do it again.
In Poul Anderson's Time Patrol series, the Patrol fights Neldorians, Exaltationists, other time criminals and even temporal chaos itself throughout history.
In Anderson's The Corridors Of Time, Wardens and Rangers wage war throughout history, hoping to influence their common unknown future.
In There Will Be Time, Havig's group must outmaneuver Wallis' Eyrie while remaining within the bounds of what is already known about future, and also some past, events. Enough remains unknown to allow them sufficient freedom of action.

