Glasgow, 1933. Murder is nothing new in the Depression-era city, especially to war veterans Inspector Jimmy Dreghorn and his partner 'Bonnie' Archie McDaid. But the dead man found in a narrowboat on the Forth and Clyde Canal, executed with a single shot to the back of the head, is no ordinary killing. Violence usually erupts in the heat of the moment - the razor-gangs that stalk the streets settle scores with knives and fists. Firearms suggest something more sinister, especially when the killer strikes again. Meanwhile, other forces are stirring within the city. A suspected IRA cell is at large, embedded within the criminal gangs and attracting the ruthless attention of Special Branch agents from London.