His life was a turbulent one: thrown in jail during the Cultural Revolution before finally being brought back to Beijing and receiving a high-ranking post in an influential police department. Now retired, however, he had all the time in the world to devote to me and my researches. He took me places in Beijing that no foreigner had ever been. From him I gained invaluable insights into Chinese history and culture, the Chinese mentality in both everyday life and police investigations. I met the most extraordinary array of people inside and outside the justice system, and remember one night being smuggled by taxi from a backstreet restaurant, where I had been questioned by the local police, to the top secret HQ of the Beijing serious crime squad off a dark alleyway buried in the depths of the city.

Usually I met Mr. Dai in the lobby of my hotel, and we would head off for our destination together on bicycles. But once I visited his home in a seedy, 1950s soviet-style apartment block, where old men played chess in the basement. And it seemed like an ignominious end to the career and life of such a noble and intelligent man.

Mr. Dai became the inspiration for Li’s Uncle Yifu.

By the time I had returned in ’97 on that first research trip, English had become more widespread. Many restaurants were now featuring menus in English or Pinyin. And those ring roads were beginning to start filling up with more than taxis and buses and official vehicles. The great move away from the bicycle towards private cars was already underway.

And during all my subsequent visits, right up until 2004, I bore witness to the transformation of a country, from the closed, almost medieval world of Mao Zedong, to the vision of modern China set in train by Deng Xioaping. Those changes are reflected in the six books of The China Thrillers, which span probably the greatest and fastest period of change in Chinese history.

As I look back now, I can see the books as bearing witness to that change. From six empty ring roads to nine ring roads jammed end to end with private and commercial vehicles. From rivers of bicycles to the merest trickle of cyclists. From the Mongolian siheyuan courtyards which had been the traditional home of Beijingers for centuries, to high-rise modern apartment blocks.

It was a breathtaking transformation, reflected in each of the books.

The “bread cars”—the ubiquitous yellow vans used as taxis, and referred to frequently in The Firemaker—had been banned by the time I returned in 1999 in an attempt to reduce pollution.

The 50th anniversary of the People’s Republic that year saw the abolition of the old green military-style police uniform, to a new smart black uniform similar to those found in police forces elsewhere around the world.