In the second of this two-part series, a group of unlikely runners living with different mental health issues are halfway through their training for the ultimate test of mind over matter. But who will make it to the starting line of one of the world's most famous endurance races, 2017's London Marathon? Mental and physical health is closely linked, and taking up sport or exercise can benefit psychological wellbeing, but this is no easy ride. Presenter Nick Knowles is on a personal mission to get the runners across the finishing line, and leads a team of running experts, nutritionists and psychologists. The remaining nine runners juggling physical injuries along with their mental health challenges and trying to fit training into their lives. They attempt longer and longer distances and even travel to the Brecon Beacons for a mountain run. The episode catches up with Rhian, Shereece, Jake and Poppy, who struggles with anxiety and the symptoms of PTSD. The runners are joined at a training day by the Duke and Duchess of Cambridge and Prince Harry. The royal trio have launched a campaign to remove the stigma around mental health issues and are keen to meet the runners and learn more about their experiences. It's an incredible boost to the runners, but will it be enough to get them to the finishing line of the London Marathon? The runners are taking part in the London Marathon for Heads Together, the campaign led by the Duke and Duchess of Cambridge and Prince Harry, which is the official Charity of the Year for 2017's event.