From publisher blurb:
Play a time cop, a chronologist or a period actor, travel back in time and fight villains intent on committing crimes throughout time!
Time Police is a d20 mini-game designed to let you and your gaming group try something different for a quick session, with the option of developing into a more long-term campaign. Time travel is one of the most classic elements of science fiction, and its mind-bending ability to mix anachronistic elements into the same story has the potential for memorable adventures. Crime in time is just the basis for this mini-game, and we encourage you to use this book to play all manner of time travel games.