Searching For Old Movie Missionary China Adopted Chinese Son Communist Revolution

I saw a bit of a movie on TV when I was a kid, probably early 70s, although the movie itself is possibly older than that. The part I saw was told in flashback: a white Christian missionary in China had adopted a Chinese boy, and at the time the boy had grown up, the Communist revolution was taking place. The missionary was arrested and put in prison, and while he was in prison he saw his son, now a prison guard. The son was cold and distant to him publicly, but later came to his cell privately and expressed anger. The son said he was doing his duty. "To God?" the father asked. "To my country!" the son shouted. He said bitterly that he had been taught to worship a God with a white face, and that the place of honor in the church was held by a white man. Later in the conversation the son calmed down and told his father he had come to try to convince him to say or do something that might lead to his release. Then it was seen that the conversation was overheard, and the son was taken away and shot (off screen; you only saw the father's reaction to the gunshot.) It's many years later as the father is telling this story and of his grief. I have no idea what the overall movie was about, or how this part that I saw fits in. I would much appreciate finding it again, though!