Knockout Week continues, with the eleven remaining contestants facing a baptism of fire as they are split into two groups and tasked with running a professional lunchtime service on their own. In this episode, the first group heads to a London restaurant headed up by award-winning chef Stevie Parle. During a busy service, the five amateurs are responsible for serving up every dish on the menu to paying customers. Who will falter as they cook in a completely unfamiliar and demanding environment? Then it's back to MasterChef HQ for an Invention Test to show John and Gregg just what they have learnt. In a last-chance bid to stay in this year's competition, each contestant has to show they can invent an exceptional dish that is worthy of gracing the table of a professional restaurant. In an unexpected twist, the contestants discover that they not only have to present their food to John and Gregg, but also a guest judge who will be helping John and Gregg evaluate the five amateurs - the formidable Professional MasterChef judge, two Michelin-starred Marcus Wareing. After this, one of them will be going home. Who will crumble under the pressure and who will make it through to Friday's challenge - the gateway to this year's semi-finals?