A group of obese teenagers tackle their weight issues at a summer camp. Katie's happy and confident on the outside, but admits that her sense of humour is a form of self-defence.

For five long weeks every summer, an elite boarding school near Leeds is transformed into the base for a unique summer camp for teenagers with obesity. For most of the campers it's a last resort in their battle for health. But it's not just their fitness that is at stake - most have suffered severe bullying, social exclusion, anxiety and depression.

The camp takes a dynamic approach - every day is packed with physical exercise and sessions designed to help with nutritional knowledge and development of self-esteem. Meals are strictly calorie-controlled and there are weekly weigh-ins to measure progress. The rules on behaviour are tough and no phones, television or internet are allowed.

In this opening episode of two, we meet 15-year-old Katie who weighs 17 and a half stone - she's confident and happy on the outside, but admits that her sense of humour is a form of self-defence. Katie has tried countless diets and is desperate to break the cycle of compulsive eating. But her attitude to the rigorous exercise programme on camp doesn't inspire confidence.

At 19 and a half stone, 14-year-old Lana is the heaviest girl on camp. She acts as a carer for her disabled mum and life has been tough for her. Can she find a new confidence in just five weeks? Meanwhile, 15-year-old Adam who weighs 20 stone, struggles with camp from the start - he finds the rules repressive and just wants to go home. His mum, whose biggest fear is that her son will die before she does, refuses to let him return. But eventually, Adam takes matters into his own hands.