The film tells about the US-Vietnam War of the late 60's - early 70's of the last century. A caravan of Vietnamese guerrillas is moving along the Ho Chi Minh trail. Among them there is an American actress and singer Kate Francis, who came to Vietnam to tell the truth about this war on her return home. In Hai Phong Mai, a Vietnamese friend of Kate, introduces her to her husband sapper Fong, who has just returned home from the Soviet Union on a merchant vessel "Chelyabinsk". Miraculously friends manage to prevent an explosion in Hai Phong port, prepared by U.S. intelligence agencies.