On the northwest frontier of India during the British Raj, Scottish Canadian Lieutenant Alan McGregor (Gary Cooper), in charge of newcomers, welcomes two replacements to the 41st Bengal Lancers: Lieutenant John Forsythe (Franchot Tone) and Lieutenant Donald Stone (Richard Cromwell), the son of the unit’s commander, Colonel Tom Stone (Guy Standing). Lieutenant Stone, a “cub” (meaning a newly commissioned officer), eagerly anticipated serving on the Indian frontier, particularly because he specifically was requested and assumed that his father sent for him; Lieutenant Forsythe, an experienced cavalrymen and something of a teasing character, was sent out as a replacement for an officer who was killed in action. After his arrival Lieutenant Stone discovers that his father keeps him at arms length, wanting to treat him the same as he treats all of the other men. He also reveals that he did not request his son serve in his regiment, a discovery that breaks his heart and leads to him going on a drunken bender. Attempting to show impartiality, the colonel treats his son indifferently. The Colonel’s commitment to strictly military behavior and adherence to protocol is interpreted by young Stone as indifference. He had not seen his father since he was a boy and had looked forward to spending time with him.
Lieutenant Barrett, (Colin Tapley) disguised as a native rebel in order to spy on Mohammed Khan (Douglass Dumbrille), reports that Khan is preparing an uprising against the British. He plans to intercept and hijack a military convoy transporting two million rounds of ammunition. When Khan discovers that Colonel Stone knows of his plan, he orders Tania Volkanskaya, a beautiful Russian agent, to seduce and kidnap Lieutenant Stone in an attempt to extract classified information about the ammunition caravan from him, or use him as leverage to attract his father. When the colonel refuses to attempt his son’s rescue, McGregor and Forsythe, appalled by the “lack of concern” the colonel has for his own son, leave the camp at night without orders. Disguised as native merchants trying to sell blankets, they successfully get inside Mohammed Khan’s fortress. However, they are recognized by Tania, who had met the two men at a social event. McGregor and Forsythe are taken prisoner.
During a seemingly friendly interrogation, Khan says “We have ways of making men talk,” the first time such a phrase was uttered in film or literature. He wants to know when and where the munitions will be transported so that he can attack and steal the arms. He has the prisoners tortured for the information. Bamboo shoots are shoved under their fingernails and set on fire. McGregor and Forsythe refuse to talk, but the demoralized Stone, feeling rejected by his father, cracks and reveals what he knows. As a result, the ammunition convoy is captured.
After receiving news of the stolen ammunition, Colonel Stone takes the 41st to battle Mohammed Khan. From their cell, the captives see the overmatched Bengal Lancers deploy to assault Khan’s fortress. They manage to escape and blow up the ammunition tower, young Stone redeeming himself by killing Khan with a dagger. With their ammunition gone, their leader dead, and their fortress in ruins as a result of the battle, the remaining rebels surrender. However, McGregor, who was principally responsible for the destruction of the ammunition tower, was machine gunned as he blew up the tower, then died in the subsequent explosion.
In recognition of their bravery and valor in battle, Lieutenants Forsythe and Stone are awarded the Distinguished Service Order. McGregor posthumously receives the Victoria Cross, Great Britain’s highest award for military valor, with Colonel Stone pinning the medal to the saddle cloth of McGregor’s horse as was the custom in the 41st Lancers (according to the film).