With Edgar teaching journalism at Yenching University, the couple turned their home into a gathering place for student activists. Among them was Huang Hua, who would be appointed the People's Republic of China's first permanent representative to the United Nations in 1971.

In June 1936, Edgar left Beijing for the Communists' base in the Northwest, where he would become the first Western journalist to interview Mao, leader of the Red Army. A picture he took of Mao in army fatigues would become the defining image of Mao for Western audiences for many years to come. And he would come back to write Red Star Over China, published in 1937, which gave the world its first glimpse into "the mysterious guerrillas that no one had written about", as An put it.

Helen's contribution was immense.

"Little was known that in September 1936, three months after Edgar left, Helen made her own first attempt to reach the Communists. For various reasons, she stopped in Xi'an, where she interviewed the Nationalist general Chang Hsueh-Liang, the 'Young Marshal' who was a secret sympathizer of the Communists," An said.

Helen listened while Chang talked about his thinly veiled desire to work with the Communists and fight the invading Japanese. Because her report could not be sent out from the Nationalists-controlled Xi'an, Helen sneaked back to Beijing to file her story for the Daily Herald in Britain.

That was a little more than two months before Chang seized the Nationalist leader Chiang Kai-shek in a military coup known today as the Xi'an Incident, forcing him to form a coalition with the Communists.

Not entirely satisfied with her first trip, Helen, mesmerized by what Edgar had to tell about the "Reds", embarked alone on her second journey, made all the more dangerous by the attention generated by her husband's previous trip. This time she made it.

She stayed in Yan'an for nearly five months, documenting the lives of not only the army leaders including Mao and Zhu, but also the wives, children and the common soldiers. A large chunk of those interviews and observations went into Edgar's book, to which Helen also contributed half of the pictures.

"They were always working as a team," An said. "After Edgar left for Xi'an in 1936, he wrote to Helen asking for an interpreter. Helen sent Huang, who went and stayed with the Red Army from then on."

Despite all that, for many decades Helen remained-and many believe still remains-in the long shadow Edgar had cast, although they divorced in May 1949, and Edgar married the actress Lois Wheeler (1920-2018) soon after.