Sue Broom investigates the world of the sniffer dog. She visits Bas Wood and his golden labrador Hattie, one of 16 Fire Investigation Dog Units operating in the UK. Hattie can find a drop of petrol in a burnt-out house, making the investigation of possible cases of arson rapid and relatively indisputable. She finds out if any dog can be trained as a detection dog, or whether it takes a special breed or individual to make the grade.