"The western people say that they were brainwashed, but they were not. They were well trained intellectuals. They knew what's right and wrong," said Fred Engst, American, son of Erwin Engst and Joan Hinton.

In the 1930s, Erwin Engst, a UN staff member, inspired by the book, "Red Star over China," came to China. His girlfriend, Joan Hinton, a nuclear physicist who once joined America's Manhattan Project, later also left the US for China.

Why did the couple leave their home country and well-paying jobs to spend the rest of their lives in China? This video documents their story.