The “X. Y. Z.” referred to had made himself manifest three days before, while Jack and Tom were conducting some experiments with their sending apparatus. In the midst of their work a confused sound had broken in upon them, and Jack, on tuning his apparatus to catch the “stranger” waves, had intercepted an apparently meaningless message signed X. Y. Z. The message consisted of a jumble of numerals which, the two lads had little difficulty in deciding, was a code of some sort. The catching of such messages being common enough in the north, they gave the matter little more thought and, in fact, till Jupe mentioned it. Jack had not recollected the occurrence at all. Now, however, as Jupe moved off forward to complete his work, he caught himself wondering who X. Y. Z. might be. He wished that they had taken down the intercepted message and devoted some of their leisure time to deciphering it; but the urgent business now in hand soon drove such thoughts out of the young navigator’s head. Tom reappeared on deck, the inevitable bit of waste in his hands. “I’ve adjusted the magneto,” he announced, “and I guess we’re turning over a bit faster than ordinary.” “Good for you,” nodded Jack approvingly, “every minute counts on a job like this.” At every turn of the shaft Jack’s heart was bounding with keen anxiety. The same might be said of Tom’s condition. The very vagueness of the message from the air, fraught as it was with the sense of disaster, added to their mystification and eagerness to reach the scene. But mingled with all this, as the two lads stood side by side on the miniature bridge of their speedy little cruiser, was a fierce sort of pleasure as they sped through the rolling swells of the gulf, hurling white masses of foam aside from the sharp “cutwater.” Behind them the coast line lay like a dim gray scarf stretched along the blue horizon. The keen, ozone-laden wind struck their faces with an invigorating tang. It was great, glorious, exciting to be out here on the broad bosom of the gulf, guiding a speedy motor craft toward unknown adventures. The zest of achievement, the glory of grappling with obstacles as yet unseen and hardly guessed at, ran hot in both boys’ veins. Fast as the _Vagrant_ was, she seemed to them to crawl, and yet, thanks to Tom’s skill as an engineer, she was reeling off her thirteen knots with the regularity of a sleeping infant’s breathing. “Jupe!” called Jack presently, “come aft and spell me at the wheel for a while. I’m going to send a few questions into the air,” he added to Tom. “Good. We’ve got plenty of ‘juice.’ Shall I go below and send up the mast?” “Yes. Better run it up to its full height. It won’t hurt in this light breeze, and I want all the radius I can get.” “Right you are.”