Ten volunteers spend five days together in a house in Cornwall, doing group tasks and being interviewed on camera. Five of them have been diagnosed with a psychiatric condition, ranging from OCD to bipolar disorder to Asperger's; five have no history of mental illness at all. Three expert psychiatrists watch the footage without meeting the group in person and try to work out who belongs in which half, using only behavior, conversation, and the tasks set for them, from a treasure hunt to a public speaking challenge. The volunteers narrate their own experiences directly to camera, describing what living with their diagnosis actually feels like day to day, while the experts occasionally guess wrong in ways that expose their own assumptions about what mental illness is supposed to look like. The format turns diagnosis into a kind of experiment on the diagnosers themselves, and the reveal at the end of each episode is less about the volunteers than about how unreliable the outside view of mental illness can be.