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.