A Secret Service operative is entrusted with plans by the U.S War Department of the utmost importance, that he is to deliver in a Pacific Coast city. Spies of a neighboring nation have an inkling of their transmission, but their opportunity to seize them does not come until the last moment as the plans are about to be delivered. Mounted officer Flynn happens in and hears just enough of the reported loss to form the quick conclusion of the natural detective. He clatters away down the street and out into the lonely suburbs over his long dark beat with all of his senses tingling with the sensation of something imminent. He is passing an unoccupied cottage when his suspicions are aroused by a light momentarily illuminating the window, like the flash of a match. He dismounts, ties his horse and creeps up to the window. He surmises the two men he sees inside are the spies who have halted for a rest before sneaking on over the border. They are nervous and alert and his discovery is coincident with theirs. The man with the plans makes his way out of the rear window; the one with the gun waits at the door ready to give the butt any one entering. When the light goes out Flynn jumps for the door and with the skill of a "half-back" splinters it from a shoulder shove. The man inside hits the officer's wrist, sending his pistol flying and tries to club him with his own weapon. In the struggle that followed all the fighting blood is up in Flynn, and he drags the armed man out into the yard, and the pair wrestle desperately on the brink of a well. With a mighty wrench he throws the weapon of the spy into the well and sends the owner after it. The spy who escaped with the plans has a good start. Flynn flings himself automatically into his saddle and starts on the race for the border. The man in front is desperate, well mounted and armed; the mounted officer gains breath as he races along, is unarmed, but unafraid. The spy turns in his saddle and fires. Flynn ducks down and lies along the neck of his horse, Indian fashion, and rapidly coils the riata that touches his thigh on the saddle. The bullets bum over him like angry bees closer and closer draw the riders. Suddenly Flynn rises in his stirrups and throws his riata. He gets a plug in the left shoulder, but the flying noose settles about the man ahead. The noose tightens and pinions the arms of the spy to his sides. Flynn closes up alongside, twists the smoking revolver from his hand, stuffs it in his own empty holster and drags the documents from the mussed-up spy. He brings the Government back its own and more; he wins a Congressional medal and only says he merely worked along the line of duty.