From the introduction: A Nineties rave drug called Reverb is back on the streets, better and stronger than ever. Now, its users and dealers have started vanishing. The Agents must identify and stop the source of the unnatural drug before anyone else falls prey to it. This scenario is meant to introduce new players and new Agents to Delta Green. It focuses on concepts that may be familiar to old hands: the Tcho-Tchos, the Liao drug, and the diluted version of Liao called Reverb. It takes place nominally in Chicago but could be played in another big city.