Hugh's fish fight goes global as he starts to investigate the problems with tinned tuna, before crossing swords with his old adversary, Tesco.After finding out that sharks, turtles and rays get caught up in the purse seine nets which supply the majority of tuna to the UK supermarkets, Hugh heads to the Maldives in search of an alternative, and finds one of the most pristine, and well-protected marine environments on the planet; and a sustainable, ethical, source of tinned tuna, caught by traditional pole and line methods.Meanwhile, some friends from Greenpeace launch their own investigation into the source of Tesco's tuna. And what they find out in Ghana gives Hugh all the evidence he needs to call for a much anticipated meeting with his old friends at the supermarket.