Horizon follows three people living with voices, hallucinations and paranoia, to explore what causes this kind of phenomena. Providing a rare first-hand insight into these experiences, they reveal just what it is like to live with them day-to-day. They examine the impact of social, biological and environmental influences on conditions traditionally associated with insanity, such as schizophrenia and psychosis, and within the film they look at how new ways of understanding the brain are leading to a dramatic change in treatments and approaches and examine whether targeting the root causes of psychosis can lead to recovery. Above all, they try to uncover why it happened to them - and whether it could happen to you.