A look at the work of the Metropolitan Police dog unit - 300 dogs and their handlers tackling crime in the capital in their own unique way. During the day, spaniels are sniffing out drugs on the streets of Camden, while in the dead of the night, German shepherd dogs will 'track and attack' armed robbers. These canines and their handlers are in the front line of the battle against crime in London.

London's Metropolitan Police Dog Unit tests the skills of its leading specialist search dogs, pitting spaniels Diesel and Billy against each other as they hunt for hidden heroin. On the streets of north London, shift leader Pete Madden puts his Alsatian Brodie in the line of fire when they target two armed robbers, but as the trail runs cold they find themselves in pursuit of a gang of car vandals