Poitier plays a Korean War sergeant commanding a small, isolated and decimated platoon of American Marines. The film explores the racial integration of the American military, centering on the African-American sergeant's struggle to win the trust and respect of the men in his unit.
When the platoon's lieutenant is mortally wounded in an ambush, he passes the role of platoon leader to the next highest ranking man, Sergeant Towler (Poitier). Towler initially feels the role should be taken by the combat experienced Sergeant Kincaid (Ladd) who has eleven years of service as a Marine. However, Ladd lost his former rank through misconduct. Ladd's prowess as a hero is demonstrated in the opening battle scene where he picks up a M1919 Browning machine gun and fires it from the hip into charging North Korean hordes.
Before he dies, the Lieutenant reminds Poitier that he is next in line for command, not Kincaid. One of the platoon, Pvt Bracken (Paul Richards), openly questions Poitier's authority in favour of Ladd.