The four remaining contenders face two more culinary challenges as they battle for a place in the semi-finals. First they are split into two groups for a test of teamwork and communication. One duo has to master John Torode's dim sum selection, and the other his spiced duck noodle broth. Then, the celebrities' team work skills are pushed to the extreme as they are faced with their first Mass Catering Challenge, cooking lunch for over 100 staff at Acton Works - the central hub for repairs and upgrades to London Underground trains.