Two Michelin-starred chef Marcus Wareing, the formidable Monica Galetti and MasterChef's seasoned diner Gregg Wallace seek out up-and-coming culinary stars. The week's best chefs return for the quarter-finals and this is where the battle really begins. Their first challenge is an Invention Test - but this one has a twist. The quarter-finalists must create an exceptional plate of food from the kitchen offcuts and trimmings. Gone are the selections of quality ingredients they are used to cooking with. Instead, the judges ask them to make their dishes from kitchen scraps, including bones and offcuts, fish skins, overripe fruits, cheese and stale bread. It's a daunting challenge and the price is high - after judging their dishes, Marcus and Monica will decide who is worthy of continuing in the competition. Next, the chefs face the terrifying task of showcasing their skill to three of the country's toughest restaurant critics. With a semi-final place at stake, the chefs have an hour and 15 minutes to create a stunning two-course menu that will determine their MasterChef future. Sitting in judgment of their culinary abilities are critics Charles Campion, Tracey MacLeod and Jay Rayner. Only the most exceptional chefs can make it through to the semi-finals and move a step closer to the coveted title of Professional MasterChef 2014.