Natasha Walter didn’t listen when her mother, Ruth, talked of killing herself. She’d been saying it for years and though she complained of suffering from dementia there had been no formal diagnosis and her memory lapses weren’t unusual for a 75-year-old. Besides, would someone so timid and anxious have the nerve? Ruth loved her two daughters and her grandchildren, and she thought of her life as happy: why bring it to a premature end? But there had been warning signs: the pieces of jewellery she gave away; the lunch to which she invited all the family despite the lack of...