China, 1926. The country is torn by revolution and exploited by foreigners. Jake Holman, an American sailor who serves as an engineer aboard the U.S.S. San Pablo, a gunboat which patrols the Yangtze River simply to maintain an American presence in China, wants no part of the whole messy situation and would prefer to simply stay below deck and keep the engines running. He is more at home with machines than people. He is forced to get involved when the gunboat is sent to rescue a group of missionaries upriver at the China Light Mission. Holman is made a part of the landing party and assigned to escort the missionaries back to the safety of the San Pablo. The spiritual life espoused at the mission affects him and draws him out of his shell. For once in his life, he feels a sense of belonging and falls in love with one of the missionaries, young Shirley Eckert, drawn to her innocence and compassion. Unfortunately, the lives of everyone there may be in danger due to the unstable political environment.