A half-Indian, half-British soldier is given command of a native fighting unit by the ruling British to squelch the uprisings of a rebellious guerilla group.

In 1857, British officer Capt. Alan King is leading a supply column to the Peshawar garrison when he is attacked by Indian rebels organized by Khurram Khan. Just before the attack, King is warned by Ahmed, one of Khan's men, and King is able to minimize the damage to his forces, which are saved by reinforcements. The garrison soldiers are led by Lt. Jeffrey Heath, who caustically states that all "natives are the same under the skin," even those in British uniform. Heath informs King that Khan has been harassing the British for a months, and that because his stronghold is in the treacherous Khyber Pass, they have been unable to defeat him. Upon reaching the garrison, King reports to Brig. Gen. Jonathan Maitland and informs him that the common people, rallied by "mullahs," or holy men, are rising up against the British, as are insurgents such as Khan. Ahmed, whose brother was murdered by Khan, warns the British officers that "the night of the long knives," during which the rebels will kill the colonialists, is coming, and asks to join the Khyber Rifles, a famed group of native volunteers. After King leaves to settle into his quarters, which he is to share with Heath and Lt. Baird, Maitland receives word that they will soon receive a shipment of the superior, new Enfield rifles. In their bungalow, Heath admires King's pocket watch but is disturbed by the portraits of King's parents lining the watch, for although his father was a British officer, his mother was Indian. King explains that his parents were killed in the rebellion of 1833 when he was a child and that he was reared by a kindly Indian man. After King leaves for Peshawar to find Hamid Bara, his foster father, Heath asks to be reassigned to other quarters. King learns that Bara is now a priest and that his son Hassan, whom King considers his brother, has vanished. King then comes across Maitland's daughter Susan and her servant, Lali, in the midst of an angry crowd listening to a mullah railling against the British. King whisks Susan and Lali to safety, and back at the garrison, learns that Heath has left their quarters. Baird, however, assures King that he does not mind his half-caste status, and that night, Maitland invites King to dinner to thank him for rescuing Susan. Maitland puts King in charge of the Khyber Rifles, who are excellent fighters despite their lack of discipline, and King reveals that he has learned that Hassan is now Khan. Later, King has trained his troops well, and an admiring Susan tells him that she has saved several dances for him at that night's ball. Susan is puzzled by King's restrained response until that evening, when she discovers that because he is part Indian, he is not allowed to enter the officer's club and attend the ball. Infuriated by the racial prejudice, Susan storms out of the club to find King, who assures her that he has learned to tolerate such slights. The couple enjoy a romantic waltz, and the following day, Susan sneaks out of the garrison to follow King as he rides to Peshawar. King relates his parents' story, and later, as they are returning home, takes shelter with Susan in some ruins when a sudden storm arises. Just before the storm hits, several native riders attack and demand Susan as a hostage, but King fends them off. Later, Maitland sends out several patrols to search for Susan and King, who are found by Heath and brought home. Realizing that Susan has fallen in love with King, Maitland decides to send her back to England, and when he obliquely hints to King that he does not want Susan to become involved with "things Indian," King understands that Maitland is referring to him. Susan is outraged upon learning of her father's plan and accuses him of being a hypocrite. Meanwhile, one of the men from Baird's patrol arrives at the garrison, and on his dead body is a note from Khan, stating that Baird and the other hostages will be exchanged for the Enfield rifles. Maitland reluctantly orders Heath to divert the shipment away from the usual route, and King offers to go to Khan's stronghold and kill him, even though the mission will mean certain death. Maitland refuses, after which King pleads with Susan to go to England, even though she loves him. When King finally admits that he loves her, too, Susan states that she will leave, but will return when he is ready. Maitland sees Susan leaving King's bungalow, and the next morning, decides to send King to kill Khan. King has already left, however, and upon reaching Khan's camp, swears that he was not sent by his commander. Telling Khan that he has deserted because of the racism he can no longer tolerate, King is accepted by the wary Khan, who boasts of his plans to control India. Late that night, King crawls into Khan's tent and is about to stab him when he hesitates long enough for Khan to awaken and escape. The following day, Khan orders Baird and the other soldiers tied to stakes, and they are speared to death as King watches. Khan spares King's life, however, just as King had spared his, although Khan warns him that there are no longer any ties between them. King is placed under arrest upon his return to the garrison, as Maitland does not believe his story, especially his claim that Khan has a plan to prevent the Khyber Rifles from using the Enfields. Disappointed, King is returning to his quarters when he learns from Heath that the women have been evacuated, and that Susan left a message for him that nothing had changed between them. While a dispatch rider brings news of mutinies across the frontier, Maitland's servant, who is secretly working for Khan, tells the Khyber Rifles that the Enfield cartridges are greased with pig fat. Because the ends of the cartridges must be bitten off before loading, the soldiers' religious beliefs will be violated by tasting the pig fat. Learning of the rumor, King explains to Maitland that the Indians are refusing to use the Enfields, then tells his men that the rumor is false, and demonstrates by loading one of the rifles himself. The men agree to follow him on a mission to stop Khan before he joins the other mutineers, and soon they are scaling the cliffs behind Khan's camp. Once they reach their position, the men refuse to use their rifles, but vow to follow King and defeat Khan's troops using only their knives. Following a bloody battle, the Khyber Rifles are triumphant, and later, after Susan's return, she watches with pride as King leads his men in a parade before the officers.