To many, Zanzibar's sandy beaches and crystal-clear waters seem like a picture-perfect paradise. Yet behind the confines of the chic hotel bars and pools, a growing number of locals are going through a heroin-induced hell - and it's one that's cheap to come by. Naomi Conrad and Michael Hartlep went to one of the island's so-called sober houses that try to wean the population off the lethal drug.