In Beijing Liubukou Chongde Middle School in 1930s, there were two childhood friends, Yang Zhenning, two years older, and Deng Jiaxian, two years younger. They are the children of Yang Wuzhi, a professor of mathematics at Tsinghua University, and Deng Yizhe, a professor of philosophy. Decades of friendship began with the tree catching cicadas and the mud playing with glass balls. This friendship has extended to the other side of the ocean. 1950, Deng Jiaxian, who was about to return home with a doctorate, broke up with Yang Zhenning and Yang Zhenping in Chicago. There was no news of Deng in the next twenty years.

1972, Yang Zhenning came to China for the second time. The authorities approved Deng Jiaxian to receive his childhood friends in his home. The old furniture was hurried away. Specially sent carpenters to polish an old bookcase in Deng Jiaxian, hastily put on a mirror, and made a "brand-new" wardrobe in one day; The worn floor was waxed, and someone moved the sofa from the office, bringing excellent varieties of watermelon, chocolate and a box of soda. It's like setting a scene on the stage. Deng Jiaxian acquiesced.