Helen Foster revealed the secret to the success of the fourth front Red Army

Through lengthy interviews and close contacts with Mao Zedong and Zhu De, Helen found that camaraderie among leaders of the CPC was an important factor for the succession of victories secured by the Fourth Front Red Army, with Zhu De as the army commander and Mao Zedong as the Party representative. Zhu De and Mao Zedong, who were vilified by the Kuomingtang, were the ones who could truly save the Chinese nation at the critical moment. She wrote in her manuscript that without Zhu De and Mao Zedong, the history of the Communist movement in China would be unimaginable. Mao Zedong had a calm political mind while Zhu De had a fiery heart as a fighter, which had kept him going throughout his life. In Helen's view, Zhu De and Mao Zedong could be seen as one. Mao Zedong was the brain, the theorist while Zhu De was the heart and the army. In her notes, Helen wrote wittily that they were both made of high-quality materials.

In addition to Zhu De and Mao Zedong, Helen also seized the opportunity of the the CPC National Congress convened in Yan'an to have long talks with many CPC leaders, which left her with dozens of thick notebooks. Later, based on her experience in Yan'an, Helen wrote Inside Red China and Red Dust: Autobiographies of Chinese Communists, unveiling to the world the town of Yan'an and the Chinese Communists.