Anorexia, the pathological fear of eating and gaining weight, is now the most deadly mental illness in the UK, affecting around one in every 250 women. In this film, Louis Theroux embeds himself in two of London's biggest adult eating-disorder treatment facilities: St Ann's Hospital and Vincent Square Clinic. As he spends more time with patients both on and off the wards, he witnesses the dangerous power that anorexia holds over them, and finds himself drawn into a complex relationship between the disorder and the person it inhabits.