Louis Theroux presents the first of two films looking at the issue of law and disorder in two volatile and crime-ridden cities – Philadelphia and Johannesburg.

In this film, Louis joins the Philadelphia Police Department to experience front line policing American-style. In the most dangerous areas of the city, there are approaching 400 homicides a year and drug dealers on every corner. It is also considered part of normal life to carry a gun.

Embedded within the Philly rapid-response teams, Louis feels a palpable sense of adrenalin mixed with frustration as police take on gangs and dealers night after night. He sees a world in which battle-hardened officers cruise the streets on constant gun alert, chase down dealers and patrol a community they feel they can never afford to trust. Day in, day out, this life inevitably takes its toll on officers who, just like those they are policing, find it very difficult to ever feel truly safe in the city they are supposed to make safe.

Louis also meets the victims of crime and people on the other end of hard-line police tactics: drug users, dealers and an increasingly cynical public who, with every police raid, grow more determined not to cooperate or “snitch”.

This is a community in which the more the police try to contain lawlessness, the more they alienate the very community they are trying to protect. It is also one in which a new drug dealer rises up to replace each one that is arrested. But Louis also finds a police officer – with years of experience – who seems to have won the trust and confidence of the people on the street, and a local street boss who has imposed his own strange version of law and order on his corner of the city.

Sunday 30 November
9.00-10.00pm BBC TWO