Lambeth Hospital has pioneered the use of short-stay emergency wards for patients in crisis. It's run like A&E but for people with mental illness. Cameras are granted access for the first time to a world where psychiatrists and nurses take critical decisions about risk every day. Over the course of a few days clinicians assess whether patients are stable enough to return home or if they need to go on to a longer stay psychiatric ward. Most patients are considered a danger to themselves or others.