Story of trooper who took part in the controversial U.S. military expedition against Mexican revolutionary Pancho Villa in 1916 that brought the United States and Mexico closer to war when Mexican government troops attacked U.S. Brigadier General John J. Pershing's force at Carrizal, Mexico. "A Trooper of Troop K" deals with a massacre of African-American troops in the Army's 10th Cavalry during the U. S. campaign against Mexican bandits and revolutionaries in 1916.