Matilda and the Ramsay Bunch are on tenterhooks as Tilly's big sister Megan takes part in one of the world's most grueling races - the London Marathon. Megan needs all the help she can get to pull it off, so Tilly and the Ramsay Bunch spring into action. Tilly takes care of Megan's food, cooking a classic athletes pre-race supper, a superhealthy carb-loaded pasta dish and an inspirational marathon pudding. Meanwhile, Jack and Holly work on motivating Megan and put together a star-studded film with good luck messages from Olympic champions Mo Farah, Tom Daley and Joe Clarke. Then it's race time! Will Megan complete the punishing 26-mile race and become the marathon girl?