U.S. Government surveyor John Field suspects Nanette, the adopted daughter of Cavalry-Major Webb, of being a spy and disclosing government secrets to the Sioux tribe, in their war against the whites. The Sioux attack and Field sees Nanette talking to an Indian, Eagle Wing during the attack. Field and Eagle Wing fight and the latter is killed. Field brings his body to the fort and Major Webb sees that it is long-lost black-sheep son who has turned renegade. Nanette then tells Field that she has been giving Eagle Wing money to keep him quiet and not disgracing her benefactor. Major Webb then reveals, in flashback, that Nanette is not a Sioux but a white girl kidnapped by the Sioux as an infant. Field then asks Nanette to marry him.