Patrick Jane's aka "The Mentalist" had his wife and young daughter killed by a serial killer known as Red John. Jane has been working as a consultant for the California Bureau of Investigation consulting on cases, but the recurring story has been him trying to capture/kill Red John. Red John seems to have a cult following and he leaves clues for Jane, sends decoys, and a whole bunch of other random stuff.
It's REALLY hard to follow if you haven't seen almost every episode. I saw all of Season 1, but have become a casual viewer since then, watching the occasional episode with my mom. It's become too heavily serialized for it's own CBS good!