Whether it's a cheating ex, a double-crossing co-worker, or the best friend who stabbed you in the back, it's human instinct to want to get even. Though most people don't act on this impulse, there are those who are consumed with getting even. For them, what starts as a nagging bitterness evolves into obsession and results in murder. Sometimes these are cold, calculated attacks and other times they are spontaneous acts of vengeance born in the heat of the moment. "Payback" examines these crimes and those who have crossed the line to seek the ultimate revenge.