The stories take place in the years 2138-43, by which time humanity has spread across some few thousand star systems. A corporation called the World Welfare Works Association (also WWWA or 3WA) helps local systems deal with problems by sending well-armed agents called "trouble consultants" to solve crimes or mysteries, for a fee. The series focuses on a team of trouble consultants named Kei and Yuri who have a reputation for leaving a trail of destruction behind them, for which they are called the "Dirty Pair".