It's the semi-finals. Firstly, Marcus and Monica send the semi-finalists to London's Knightsbridge to work in service under one of the country's greatest fish chefs - Nathan Outlaw. Nathan earned his first Michelin star at the age of 25 and now holds three in Cornwall and one at Outlaw's, where the semi-finalists must deliver. First, Nathan shows each chef a dish from his menu, which they must take charge of in the lunchtime service. Their cooking skills, timing and judgement must be absolutely spot-on if they are to do justice to the delicate modern seafood dishes that have earned Nathan his award-winning reputation. With guests paying up to £100 a head for the chance to dine, Nathan lets nothing leave the kitchen unless it is executed to perfection. Next the chefs must prove their culinary skills once more as they cook Nathan their version of his acclaimed signature dish - turbot cooked on the bone, served with deep fried potatoes and capers, with asparagus, peas, broad beans and a warm tartare sauce. Using one of the most expensive fish available and with the added challenge of cooking it on the bone, they need to stay focused if they want to impress. Finally, the semi-finalists return to the MasterChef kitchen to cook two of the most important courses of their careers for Marcus and Monica. In this final battle for just one place in the final, they need to showcase all their skills, creativity and passion in an hour and 45 minutes if they are to convince the judges they've got what it takes to become a Professional MasterChef finalist.