Actors Sid Owen and Tina Malone, champion Paralympic swimmer Liz Johnson, BBC Breakfast presenter Louise Minchin and TV personality Amy Childs take part in the third heat.
In the Mystery Box challenge, they must create a dish using ingredients based on an American diner theme. They are then thrown in at the deep end as they take part in lunchtime service at two busy London restaurants, cooking for the public.
Then it is back to HQ as the contestants prepare a two-course meal to convince the judges they deserve to retain their place in the competition.
