 Captain Frank Casey (Jack Perrin) of the U. S. Army Cavalry, known as "Hair-Trigger", a sobriquet given to him from his WWI days because of his prowess with a Colt 45 and his sudden outbursts or temper, is given a message from the Border Patrol by his orderly Snowflake (Fred Toones billed as Snowflake). It says there is trouble down on his ten-thousand acre ranch on the border.  Pears that somebody is smuggling illegal Chinese immigrants across the border. Casey takes a ten day leave to check it out. His ranch is being run by his brother Dave (Wally Wales) and the foreman, Karney (Edward Cassidy), who was with Casey in his overseas company as a highly-trusted aide. Casey goes to dinner in Chinatown, and sees a man knock down a Chinaman and take off just ahead of a hurled hatchet. Not the last hurled hatchet in this one. Casey overtakes the fleeing man and finds out it is Karney, who gives a vague reason for being there. "Just out for a little Chop Suey, Cap. " Back at the ranch, Casey and Snowflake learn that ranch hand Slim Elkins has been killed the night before and Casey finds a clue---a silver concho.colton of the Border Patrol (Robert Walker) informs Casey that another group of Chinese is about to be smuggled over the border by a Mexican missing a concho. Cut to a Mexican releasing four Chinese from beneath a cabin, robbing them of their money, leaving them bound and gagged and preparing to take off just as he spots Casey riding up on Starlight. But Jane Elkins (Betty Mack) comes along in her sporty convertable roadster which the Mexican seizes and takes Jane along as a hostage. But Casey and Starlight take a shortcut and intercept the car, take the Mexican prisoner and he turns out to be Karney, who gets a lecture from Casey about ingratitude and treachery. Karney, not in the mood for a lecture from his commanding officer from a war that ended 18 years ago, crashes through a window and makes for a horse. Oops... look out for that hatchet! Must have been the guy he knocked down in Chinatown in reel two... the other four are still tied up. Casey has wrapped everything up in two days and decides to spend the remaining eight days of his leave with Jane.