In the last of the quarter-finals, the best chefs from the week's heats come together in the kitchen to cook against each other and continue in their quest for the title. They must prove to Marcus and Monica they are worthy of staying in the competition when they face two more challenges designed to test them further. First, is the daunting invention test. From an array of sweet and savoury ingredients, the chefs are tasked with creating one incredible dish with either herbs, citrus or spices as the core central theme. With 10 minutes to choose ingredients and just 70 minutes to cook it, the pressure is immense to create a dish that will win over Monica and Marcus and prove that they really have the skills and experience to carry them through to the next round. Will they remember to allow their chosen hero ingredients to shine through their dish? They have to keep their focus and remain calm as, at the end of this challenge, two chefs will be chosen to leave the competition. The remaining four chefs now face one of the toughest rounds of the competition. In an hour and 15 minutes, they must serve up an exceptional two-course menu to three of the country's most notable restaurant critics - Jay Rayner, Grace Dent and Amol Rajan. This culinary trio is accustomed to eating the most daring and delicious food in the very best UK restaurants, and this is the one and only chance the chefs have to pull out all the stops in order to impress them. Monica and Marcus will be keeping a close eye on them as they work in order to judge who shines through and provide the most creative and technically accomplished menu for the critics' table. After a tough session in the kitchen, one more chef's journey will be over when they are sent home. The three chefs considered to have impressed the critics and judges the most, survive to move on to Knockout Week and take one step closer to the final of MasterChef: The Professionals 2017.