The MasterChef semi-finals continue as the eight remaining cooks in the competition head to RAF Halton in Aylesbury to celebrate 100 years of the RAF's formation. The semi-finalists are split into two teams of four and face the enormous challenge of running their own kitchens in two specially constructed catering tents. Each team must create two main courses and a dessert to feed 120 veterans, serving airmen and new recruits for a special lunch that celebrates the centenary. With less than four hours to deliver, organisation and teamwork are essential for success. It's vital that the two teams perform at their absolute best and produce a lunch worthy of the occasion, because after judging their food, John and Gregg pick the weakest team to return to the MasterChef kitchen, where they cook-off against each other in a special Invention Test. The contestants must create a stunning dish from the leftover produce from the previous challenge, which includes guinea fowl carcasses, salmon scraps, vegetables, fruit, and cheeses. The battle is on to stay in the competition and take another step towards being crowned MasterChef champion 2018.