Take ten volunteers, half have psychiatric disorders, the other half don't - but who is who? Over five days the group are put through a series of challenges - from performing stand-up comedy to mucking out cows.

The events are designed to explore the character traits of mental illness and ask whether the symptoms might be within all of us.Three leading experts in mental health attempt to spot which volunteers have been diagnosed with a mental health condition. But will the individuals who have suffered from mental illness reveal themselves?

Ten volunteers have come together for an extraordinary test. Five are "normal" and the other five have been officially diagnosed as mentally ill. Horizon asks if you can tell who is who, and considers where the line between sanity and madness lies.