Mark Clemmit and Mark Millar continue with their quest to hunt down tradesmen who have left houses in really bad conditions. Each year around 7,500 unregistered and illegal gas engineers fit 250,000 appliances in homes all over the the country leaving lives at risk. The team go undercover to expose a serial offender who has been carrying out illegal gas work for years. Angellica is with pest control specialists as they attempt to work out how rats are accessing a family home in Swindon.