Filmmaker Konstantin Bojanov shines a sobering light on heroin's unchecked use in his native Bulgaria by following the lives of six young junkies -- a ragtag group of social outcasts who embody the city of Sofia's "invisible" population. Filmed over three years, this compelling documentary tracks the mainliners' euphoric highs and dizzying lows with unprecedented intimacy, opening the door to a discussion about the perils of addiction.