There was a mystery haunting award-winning investigative journalist Johann Hari. He was thirty-nine years old, and almost every year he had been alive, depression and anxiety had increased in Britain and across the Western world. Why?

He had a very personal reason to ask this question. When he was a teenager, he had gone to his doctor and explained that he felt like pain was leaking out of him, and he couldn't control it or understand it. Some of the solutions his doctor offered had given him some relief-but he remained in deep pain.

So, as an adult, he went on a forty-thousand-mile journey across the world to interview the leading experts about what causes depression and anxiety, and what solves them. He learned there is scientific evidence for nine different causes of depression and anxiety-and that this knowledge leads to a very different set of solutions: ones that offer real hope.