The question Cheng asked that day was provocative to say the least: “If a group of bandits broke into your home, raped your wife, killed your children, and were about to slit your throat before being subdued by the police, would the story be police brutality to you?

“Japan was aggressive. The atomic bomb was something they brought on their own. It stopped the war. It not only saved the Chinese, it saved Japanese lives also. They didn’t have to fight to the death for their emperor. It saved American lives and British lives as well. For us, the atomic bomb was a godsend. Thunders from heaven to punish the aggressor.”

Cheng says the reaction to his question in 1995 was muted at best. “I am not really sure if they heard me.” Of the four, Sodei was the “most reasonable”. He not only sought Cheng out and sympathised with his perspective, he asked if he would sign a petition urging the Japanese government to apologise for war crimes. It was, Cheng says, the “awkward silence” of the American historians and scientists that prompted him to write the novel.

“I wanted to communicate this view of history to a larger part of the world, to see there is another story.”

Drawing on extensive scholarly research and first-hand interviews with two survivors of the massacre, Nanjing Never Cries follows 18-year-old May Chen, a promising student whose life and family are shattered by the Japanese attack. Her story of courageous endurance is spliced with that of John Winthrop, an American academic on secondment from MIT, Calvin Ren, a brilliant engineer at Nanjing Central University, and Vautrin herself, the real-life president of Jinling Women’s College, who resisted Japanese soldiers almost single-handedly.

Cheng is certainly not bashful about the results. He cites a Chinese literary critic who informed him that Nanjing Never Cries is already “among the immortal novels in China”, and that Cheng himself was “one of the greatest writers in the 21st century”.

“I knew that the book would eventually become a classic in China because I spoke their minds,” says Cheng. “That is what they wanted to speak but nobody was able to.”

Although this exaggerates Nanjing Never Cries’ literary qualities, the book is nevertheless powerful and impressive. Cheng decided to write in English, his second language, which meant overhauling a prose style more suited to academic periodicals than dramatic storytelling.

Cheng realised that to do justice to the events he had to see the city for himself. “I went to live in Nanjing just to feel how people think and live. One day I feel really proud when someone asked for directions. I feel I become a Nanjingese. I was able to get into the soul and write this story.”

Most importantly of all, he spoke to two survivors, then in their 70s. Their account of the atrocity formed the basis for Cheng’s own terrifying version, which culminates in the chilling murder of May’s family.

“He was an old man, but he couldn’t suppress the emotion 60 years after the facts,” Cheng says of one survivor. “He told me what happened and how families were being killed by the Japanese. It was so real. You know he couldn’t make up the story. My wife was present. She cried.”

The writing process proved comparably affecting. “I cried sometimes. Sometimes I feel that someone was guiding my hand to write this.”

Cheng was born some 1,300km southwest of Nanjing at the very moment that the Sino-Japanese war broke out, “in the year of the Marco Polo incident”, he says, referring to the hotly debated military encounter in July 1937 that is widely regarded as having ignited the Sino-Japanese war. “I went through the eight years of turmoil. Life was very hard.”

Japan’s invasion drove Cheng’s family from Guangzhou to avoid the fiercest fighting. “The Japanese took the coastal areas, mostly the big cities. They couldn’t infiltrate too far inland. We were safe there for many years – until 1944. Then the Japanese came and we had to run again.

“After a few months the Japanese army were defeated. We never moved back.”

The Chengs may have escaped the Japanese-occupied areas, but they were regularly subjected to air raids. “I ran under Japanese aeroplanes,” he says, remembering his five-year-old self. “I was so fascinated because the airplanes would drop their bombs and it was like a line connecting the airplane to the ground. And then they exploded.”

He remembers being dragged under the flimsy protection of a bed. “It changed my perception of the airplanes entirely. I heard the bombs coming, and then machine guns. I was frightened. After the airplanes went away, the person holding me said, ‘Run for the shelter.’ We did but not before the airplanes caught up with us. Then there were explosions all around. Fortunately, I was unhurt. I saw smoke all around me. People carrying their dead to the mountains.”

Cheng drew on these experiences when describing the terror felt by his own fictional characters. “I remember how bad it smelled inside the air raid shelter. It was so dark. I was scared. Someone tells me the air raid shelter is not bomb proof. If a bomb drops, it would collapse. We would all be buried.”

Cheng is quick, however, to distinguish his privations from those of the army resisting the Japanese forces. “I did not experience the utmost hardship. We had little good things to eat, though not bad compared to the soldiers. We were full. But we never had any fruit, for example. Very rarely meat or fish.”

What proved harder to resolve were his feelings of constant fear. “It was mostly subconscious. When I would play I would forget about it. But I would have nightmares quite often – that the Japanese would break through the door and kill me and my family.”

These nightmares lasted, Cheng says, until he moved to America in 1970. Even there “I could feel the humiliation of the Chinese. The Japanese regard the Chinese as an inferior race. They could do whatever they wanted to the Chinese people. One Japanese soldier said that killing a Chinese is easier than killing a chicken. They could rape Chinese women in open daylight. You know how humiliating it is for women in the old days. For some of them it is worse than death. For the men – the husbands and fathers – you can imagine the humiliation they must suffered.”

Cheng believes this underlying national shame drove the Communist revolution and its subsequent policies. “Why would people go through the Cultural Revolution? It’s crazy. But they were so humiliated they would do anything to restore this sense of pride. Mao Zedong drove them to work hard for the nation because they felt the pride.”

I ask whether increased knowledge of Nanjing might also encourage greater awareness of present-day human rights abuses both inside and outside China. When I mention Tiananmen Square, Cheng’s forthright tone returns.

“Many people have different views about what happened in Tiananmen Square. I think Tiananmen Square has been presented by the Western journalists. They might not have seen the other side. There are many people who fear the revival of the Cultural Revolution. Many people feel that the last thing China needed was chaos. So Tiananmen Square had its good side. China probably was not ready and it’s not ready now [to liberalise].” At the same time, he concedes his surprise at “how oppressive the [Chinese] government is at the moment”. His evidence was a recent visit to China to discuss Nanjing Never Cries. His publisher asked him to send an advance copy of his talk. Cheng’s refusal prompted a panicked message.

“They said, ‘If you say anything, just one word that is offensive to the government, we could be wiped out. The whole publishing company will be forced to close down. Please be understanding.’ So I decided to send my speech to them. They were very happy. There was nothing that would cause them to be crushed.”

Cheng has lived outside China for most of his adult life, working in Taiwan before emigrating to America. It seems he views his 21st-century homeland as a place of ever-changing contradictions. On the one hand he says, “I understand what the human rights people are talking about.”

Later he amends this. “As long as the people have a good living they would rather give up a little bit of their rights. In fact, they are quite free to talk about the government in China. They are able to criticise, complain. The only thing you are not allowed is to stand on a street corner on a soap box making a speech against the government. You can talk all you want in private. They are much freer today than they used to be.”

As for Nanjing Never Cries, Cheng says that writing the novel has helped him to understand, if not forgive, the Japanese who sacked the city and bombed his family 80 years ago.

“I don’t condemn the Japanese the way some Chinese do. They are human. Before I went to Nanjing in 1999, I told my wife, ‘Don’t you dare buy a Japanese car or computer or fax machine.’” After completing Nanjing Never Cries, he tells her, “Now you can buy everything Japanese you want. I certainly came to realise that everyone is human. In certain circumstances, I could have behaved like the Japanese soldier.”

Cheng even sounds optimistic that Nanking massacre deniers in Japan will eventually be drowned out.

“The younger Japanese people are getting a little more enlightened,” he says. “I think people will eventually get to an understanding. And I am trying to do my part. I am not trying to extract a pound of flesh. I just want this history to be remembered. Then the Japanese can be forgiven and come to a closure of our chapter. I think it will happen.”