In this fictionalized story of Osceola an incompetent US Army Major tries to massacre the Seminoles in Florida and then breaks his word to Chief Osceola. Lt. Caldwell is trying to make peace but faces a court martial.
In 1835 Col. Zachary Taylor (Fay Roope) presides over the court martial of Lt. Lance Caldwell (Rock Hudson), who tells his story.
Lt. Caldwell is returning to Florida as an Army scout and is attacked by a Seminole. He reports to Major Degan (Richard Carlson), who will not talk with him until he puts on a clean uniform. Degan explains to Caldwell that they need Florida for farming, but Seminoles led by Osceola refuse to be moved out. Degan says he operates by the book, and he assigns Sgt. Magruder (Lee Marvin) to spy on Caldwell.
Caldwell gets leave to visit Revere Muldoon (Barbara Hale) and tells her the Seminoles must move within a month. She says that John Osceola decided not to go to West Point, and she gives Lance a little kiss.
Revere takes a canoe and goes to the Seminole camp, where she passionately kisses John Osceola (Anthony Quinn) and warns him. Kajeck (Hugh O’Brien) tells Osceola they must drive out the soldiers, but his father Kulak (Ralph Moody) trusts Osceola to make peace. Osceola advises Revere that Lance may be a better match for her than he.
Caldwell and a contingent find a dead Seminole, and he discovers the soldier lied about it but actually shot the Indian in the back as the four Indians were leaving to avoid conflict. Caldwell explains this to Degan, who reprimands him for taking a soldier “to task for killing hostiles.” Degan tells a meeting of officers that they will attack the Seminoles by surprise. Caldwell asks for a private meeting, which Degan refuses. Caldwell asks him to change his “extremely hazardous” plan, but he does not do so and then argues with Caldwell privately. Caldwell prepares the route and asks Magruder about Degan.
Degan, Caldwell, and Magruder lead a dozen soldiers and take a canon on the expedition. Revere arrives at the fort but learns that Caldwell left. A soldier reports that she is riding a US Army horse that was stolen.
Degan halts the march and tells them they are going on without the horses and must be quiet. Men pull and push the cannon through the swamp. Cpl. Gerard (James Best) is injured and has a fever. Degan tells Caldwell that he is an old hand at killing Indians. The cannon sinks in quicksand, and Gerard goes down with it. Degan orders Caldwell to save the cannon, but he goes under water and saves Gerard instead. Degan reprimands him for disobedience. They trudge on, carrying Gerard on a stretcher. During a rest stop Gerard starts screaming, and Degan orders Caldwell to gag him. They clean their weapons and sneak up on a Seminole camp. Degan orders them to shoot, but they find the village deserted. Suddenly they are attacked by Seminoles in the trees. They fight with bows and arrows, tomahawks, guns, and swords. Caldwell kills two Indians and is shot with an arrow. Degan is wounded and is helped away by Magruder. The Seminoles save Caldwell and treat his wounds.
Kajeck asks Osceola why he saved a white man. Osceola tells Caldwell he sent Revere with his plan for peace.
Degan has summoned Revere and asks if she visited Osceola. Degan accuses Caldwell and her of “dealing with the enemy.” He has Magruder tell her that the Seminoles spared Caldwell but killed the others. Degan asks her to persuade Osceola to come in under a flag of truce, or she and Caldwell may be prosecuted.
Revere goes to Osceola, who lets her see Caldwell alone. He is jealous, and she asks them to go back. Osceola says he will go to make peace. Osceola says goodbye to his people, but Kajeck is skeptical. Osceola with a white flag enters the fort with Caldwell. Magruder tells Caldwell that they beat up Osceola and threw him in the pit. Caldwell goes down in it, and Osceola says they wanted him to surrender his people. Caldwell complains to Degan, and they quarrel. Caldwell demands that he release Osceola and calls Degan sick. Degan slaps him and takes his stripe. Caldwell says he cannot get it without a court martial. Magruder tells Caldwell that he is confined to quarters.
On a rainy night Kajeck climbs over the wall and kills the soldier guarding the pit. Magruder releases Caldwell so that he can save Osceola. He arrives in time to stop Kajeck from knifing Osceola. The three fight. Osceola is knocked out and falls into the water. After more fighting, Kajeck escapes. Caldwell pulls Osceola out of the water and discovers he is dead.
At the court martial Caldwell says he told the truth. Taylor doubts that a Seminole killed Osceola, and the only evidence is Caldwell’s word. Degan says Caldwell committed murder and treason. Magruder admits that Caldwell was dealing with the enemy. The court finds Caldwell guilty, and Taylor sentences him to be shot.
Caldwell is about to be executed when suddenly many Seminoles appear on the walls. Kajeck comes in and speaks to Col. Taylor, admitting that he killed Osceola. Taylor lets him take Osceola’s body. He clears Caldwell and says that he will investigate Degan. The Seminoles leave with the coffin. Caldwell tells Taylor that he believes the Seminoles want to live in peace with them. Caldwell tells Revere that Osceola was a great man and loved his people. She says, “He loved all people; that’s what made him great.”
The real Osceola was captured by deceit, but he died in the fort of malaria. This drama portrays how some American officers had a tendency to mistreat Indians to get their land. Their ambition caused them to care more about their own career than about other people. Others who cared about the Indians often found themselves in difficult circumstances, while the Indians themselves faced even more adverse conditions when threatened by the expansion of western civilization.