Violence is running out of control in Mexico as rival drug cartels battle over the smuggling routes to America. Mexico's president has declared war on the gangsters but the only result appears to be an escalation of the killings. Katya Adler journeys deep into the heart of a shocking conflict, uncovering the human stories behind the seemingly random and disturbing violence. She asks whether the continuing freedom of the world's most powerful drug runner, Joaquin 'Chapo' Guzman, is evidence that the Government's war is toothless.