Louis spends time with four different patients who have sustained a brain injury at various stages of their rehabilitation, creating a poignant portrait of people caught between old and new selves.
An estimated one million people in the UK are living with the effects of a brain injury.
We'll bet you don't know everything about our favourite film-maker...
Louis Theroux traces the fortunes of different people suffering from alcoholism.
Louis meets transgender children as they undergo life changing treatment.
Louis visits Coalinga Mental Hospital, which houses more than 500 convicted paedophiles.