For the first time, a documentary reveals the inner workings of an investigation undertaken by the international justice system. The film follows the case of an investigating magistrate and his team, delegated by the UN to hunt down the main people responsible for crimes commited in Cambodia during the Khmer Rouge reign, during which nearly two million people died between April 1975 and January 1979. Shot over three years in the interrogation rooms and during reenactments on actual torture sites, the film reveals all of the regime's horror. In the presence of the regime's former leaders who are now defendants in their eighties, the case develops, eventually leading to the trial of Khmer Rouge members. This film is a unique opportunity to discover the way international justic works and what is at stake for it, set agains the background of one of the 20th century's greatest tragedies.