She rode straight down the ridge to the mail box, grimly determined to let no little clue to Johnny Jewel's insufferable behavior escape her. Johnny was up to something, and it might be that the mail box was worth inspecting that morning. So Mary V rode up and inspected it. There was not much, to be sure; merely a letter addressed to the Pacific Supply Company at Los Angeles. Mary V held it to the sun and learned nothing further, so she flipped the letter back into the box and rode on, following the tracks Johnny's horse had made in the loose soil. She was so busy wondering what Johnny was ordering, and why he was ordering it, that she had almost reached Sinkhole Camp before it occurred to her that Johnny had that unpleasant stranger with him, and that it might be awkward meeting the two of them without any real excuse. Johnny himself knew enough not to expect any excuse for her behavior. Strangers were different. But she need not have worried, for the cabin was empty. Since Johnny had not washed the dishes, Mary V observed that two persons had breakfasted. She observed also that Johnny had been in so great a hurry to get that letter to the mail box ahead of the stage that he had unceremoniously pushed all the dishes to one side of the table to make space for writing. She picked up a paper on which an address that matched the letter in the mail box and various items were scribbled, in a handwriting unlike Johnny's, and she studied those items curiously. It was like a riddle. She could not see what possible use Johnny could have for a quart of cabinet glue, for instance, or for a blowtorch, or soldering iron, or brass wire, or for any of the other things named in the list. She saw that the amount totaled a little over twenty-five dollars, and she considered that a very extravagant sum for a boy in Johnny's humble circumstances to spend for a lot of junk which she could see no sense in at all. Having set herself to the solving of a mystery, she examined carefully the blue print laid uppermost on a thin pile of his lessons and circulars. There were pencil markings here and there which seemed to indicate a special interest in certain parts of an airplane. There was a letter, too, from Smith Brothers Supply Factory. She hesitated before she withdrew the letter from the envelope, for reading another's mail was going rather far, even for Mary V in her ruthless quest of clues. But it was not a personal letter, which of course made a difference. She finally read it; twice, to be exact. Its meaning was not clear to Mary V, but she saw that it had to do with airplanes, or at least with certain parts of an airplane. She wondered if Johnny Jewel was crazy enough to try and make himself a flying machine, away down here miles and miles from any place, and when he did not know the first thing about it. Perhaps that horrid man he had brought was going to help.