It seems to have become impossible to win the battle against organized crime nowadays without using undercover practices. Agents infiltrate criminal groups and then secretly work their way up. For years, they may be in contact with leading criminals and they often have to be a criminal accomplice in order to gain confidence. Who are these people? What kind of personality do they have to want to do this and to be able to live this kind of life? What power do they derive from their undercover status and do they exercise this power legitimately? Undercover operations have resulted in spectacular successes, but also dangerous blunders where constitutional boundaries have often been exceeded. Based on exclusive shots of secret operations, of training undercover agents and of enthralling first-hand testimonies given by former European and American Undercover agents of the FBI and DEA, an exclusive picture is painted of this unknown world, the twilight zone between crime and law enforcement.