And so, the Library of Time serves as a collection of books about history, all history, including the histories that no longer happened.
However, a book that tells of an alternate timeline can be a powerful weapon in the wrong person’s hands. The very existence of a book like that warps reality around it. As such, the library sends out Agents constantly in search of these books in the wild, books which they call “Rogues.”
Those very few people aware of the Library of Time will likely only interact with it through Agents. Agents look human, but each possesses a special superpower that makes them extremely formidable.
As a friendly faction, an Agent uses the PCs to locate Rogues. Usefully, the nature of the alternate timeline in the book will shift the world around it. For a Rogue in which Ancient Greece defeated Rome and became a superpower, its owner will possess an unusually high number of Ancient Greek artifacts. For a Rogue in which Germany won World War II, a Nazi theme will prevail.
As a foe faction, the PCs need a Rogue for vital information about an important historical character who died much earlier in the actual timeline. For a modern equivalent, imagine characters investigating the Kennedy assassination who discover a Rogue in which Lee Harvey Oswald wasn’t shot.
This, naturally, puts them at odds with an Agent or two.
Keep an eye on this blog; on Monday I’ll post a stat block for an Agent.