In the early hours of the morning, a man reports a fire on two old canal boats. One of the firefighters notices the use of accelerant at the scene and calls the police, but by the time Inspector Banks arrives, the fire brigade have put out the flames and only the smouldering wreckage remains. A body has been found on each barge, and all the evidence points towards a deliberate arson attack. One of the victims is Tina, a young girl with a drug addiction and a terrible past who had been living with her boyfriend Mark. The other is Tom, an artist who had been living alone. Now, with little evidence to go on and a number of possible suspects, including Tina's boyfriend, the local 'lock-keeper' who reported the fire, and Tina's own father, Banks must begin to delve into the lives of the victims, and to discover who could have wanted them out of the way forever...