The four remaining celebrities in heat four face three more culinary challenges as they compete for a place in the last quarter-final.Their first challenge is a Knowledge and Skills Test, where the celebrities have the terrifying task of facing judges John Torode and Gregg Wallace one on one. They must demonstrate their ability to make sweet and sour prawn balls in just 20 minutes.Next, the celebrities are pushed to their limits. Up until this point in the competition, they have been cooking food as they would at home, but to show them what restaurant standard cooking is all about, John and Gregg invite in a professional chef. Anna Haugh, owner of the restaurant Myrtle in London, challenges each of the four celebrities to cook a recipe from her menu, which champions Irish produce.Then it's crunch time, with just one more chance to earn a place in the quarter-final. The brief is to recreate their favourite takeaway. With just one hour to cook, and only three quarter-final places up for grabs, the celebrities give it their all in a final attempt to prove themselves to the judges. At the end of this test, one of them will be going home.