U. S. Armsy Intelligence Service Lieutenant Jerry Burke is sent to Denver to investigate Indian uprisings and internal trouble which threaten the success of the Union cause. He is accompanied by his sidekick Gabby Whittaker. On the westward-bound stagecoach, they meet Lylah Stanford and Etta Mae. Lylah is on her way to Denver to be married. In Denver, Jerry learns that the man responsible for the Indian uprising and Secessionist propaganda is his own blood brother, who is using the name of Donald Mason, and is also Lylah's intended. Mason is in cahoots with Jim Macklin, Indian Commissioner who is secretly providing the Indians with arms. Jerry uncovers proof of his brother's treachery and Lylah is convinced of her fiance's unworthiness. Etta Mae is injured in one of the uprisings and Lylah is determined that Mason shall be brought to justice. She sets a trap for him while Jerry and his aides close in on him and his henchmen. He eludes the trap, escapes and takes Lylah with him. Jerry pursues but is shot by one of the Indian henchmen. Mason still bears a spark of love for his brother and nurses him back to health; escaping afterward and heading south to Mexico. Jerry, bound by his duty and oath, pursues Mason and overtakes him. Mason, who knows that his return will mean court martial and the death sentence, persuades Jerry to allow him to "escape"---and have him shot in flight. Jerry returns to Denver to marry Lylah.