A group of adventurous youths from a Midwestern club travel to Texas to ride with the frontier policemen and explore border country. Their journey takes them across the Rio Grande into a Mexico troubled by unrest, where meetings with a newspaperman and a mysterious young pianist draw them into escalating dangers: scouting missions, armed encounters, a stampede, kidnappings, and pursuits of suspected rustlers. The narrative traces their efforts to rescue captured friends, withstand sieges and gunfire, and bring outlaws to account, while one dramatic incident leaves a lasting mark on their impulsive, thrill-seeking companion.