Mercer and Graham have returned from South Africa and they need a favour. They are trying to do a deal to buy some diamonds from a recent robbery in, London. They are £50,000 short, so put pressure on Frank to raise the money. Seeing this as a chance to get rid of Mercer and Graham for good, Frank enlists the help of Bromley and Blake. Meanwhile, at the marina, Blake investigates a series of thefts, thefts which Metcalf has accused Senora Sanchez of being involved in.