Senator Gwin returns to San Francisco weary and dejected, having failed to convince Congress to subsidise his dream of a fast mail service from Missouri to Sacramento - the Pony Express. However, cattleman Iron Jack - former Texas Ranger and guerrilla fighter - reckons there's another way... Gwin sends him East to seek the investment of freight magnate Will Russell. But Iron Jack had best watch his step: Kansas and Nebraska have a bounty on his head - for murder!