"I used to play football." He laughed. I have always been sensible about that nickname. "Well, here's the situation. I've been at Vernon's mine in Durango, Mexico. Called El Tigre. Gold and thorium. There's a little mystery--" "Vernon? Is it Doc Vernon, the scientist. His daughter inherited a mine--" "_Si, Señor._ Ellen Vernon is some young lady!" "I knew them at Texas University. I was in Vernon's chemistry class before he went daft on his death ray machine, and left to work on that." "The Doc is still at work on the machine. In fact, that is a part of the mystery. "The mine is in an old corner of the desert, about fifty miles south of Mocolynatal--the big mountain. And there's something queer going on about that mountain! "Ellen got herself a radio set to pass away the time with. She got to picking up strange stuff. Sounds we couldn't make out! Not just a strange lingo. They don't sound like the human voice at all! Strange chirps and squeaks! Doc and I rigged up a directional set, and found that the calls were sent from Mocolynatal. "The mountain's in sight, to the north of us. I got to watching it, and found out something else. There have been airplanes flying about it--queer red machines with short stubby wings! They flew off mostly to the west. I did a little more investigation, and found that a line of run-down Jap tramp steamers has been hauling cargoes of the-lord-knows-what, and unloading somewhere along the Pacific coast of Mexico--evidently making connections with the red machines. "Now, the Doc has his machine where he thinks it will be the end of the world if anybody gets hold of it. We've seen one or two of the red planes over the mine, and he is afraid they have found out about it, somehow. He got nervous, and sent me up to see Uncle Sam. It is all news to the State Department, and we are going to investigate. "One of the Jap tramps is leaving here tomorrow, and there will be a couple of destroyers on the trail, to see what they unload, and where. I've got hold of a new airplane--a queer little machine called the Camel-back, that I'm taking along on board. A jewel for mountain work--you could land it on a handkerchief. I needed a partner, and the Doc told me about you. Want to go along?" "You bet I do! I've been longing for something to turn up." "Well, be at the landing field at nine tomorrow--this morning, rather, ready for anything. This may be interesting before we're through. _Buenas Noches._" A Raid and a Mystery