The therapist who has treated some of Britain’s most violent criminals says that understanding starts with a recognition that there is a capacity for cruelty in all of us

One of the sounds I remember most clearly from childhood is the Broadmoor siren – plangent, baleful – whining through the Berkshire mist. It was tested at 10 a.m. every Monday morning. If it went off at any other time, we knew that someone had escaped. The men who might then be on the loose included Ronnie Kray, Peter Sutcliffe and Graham Young, the “Teacup Poisoner”: people scarcely human, my schoolmates and I imagined. Monsters.

Gwen Adshead’s The Devil You Know, just out from Faber, corrects these lurid fantasies. A forensic psychiatrist and psychotherapist, Adshead has devoted her working life to caring for violent offenders, many of them at Broadmoor. And while the picture she paints of England’s oldest high-security hospital is not always happy – the “still, sad music of humanity” plays as a background refrain throughout the book – she nevertheless conveys a place of healing, hope, even “beauty”.

The men and women she treats, suffering mental illnesses such as psychosis or paranoid schizophrenia, have committed crimes including serial murder, rape and child abuse, leaving waves of unimaginable human suffering that ripple far beyond their immediate victims, into families and communities, often over several generations. But Gwen Adshead believes that for the perpetrators, “no matter what their history”, therapeutic treatment works. “If people are able to be curious about their minds, there’s a chance we can make meaning out of disorder.”