It's 8 p.m. in Chelsea, Massachusetts, just across the Mystic River from Boston. For Lt. Detective David Betz, his day is about to get busy. After about 30 minutes, Betz, head of the Narcotics and Vice Division of the Chelsea Police Department, leaves to meet with a confidential informant who has been assisting with a case. "When we make contact with this person, hopefully they will be able to make a call to any number of their sources, and we'll try to buy some heroin off the street tonight. ... This is basically the meat and potatoes of what we do," Betz says.