It happened, at this particular moment, that all the operators' positions on the road were filled by competent men, and so Allan had to wait until some one of them was promoted or resigned. As for Jim, he had reconsidered his decision to become an operator. He had a natural love and aptitude for machinery, and he finally determined to remain in the branch of the service where he was, and seek promotion where he would probably deserve it most. But Allan's mind was made up, and he lost no opportunity to perfect himself. Often, after supper, he would return to the dispatchers' office and prevail upon the night operator to permit him to attend to his work for awhile, and in this way he got valuable practice; but he longed for the day when he should be given a key of his own--when the responsibility would be all his. The chance came at last. He was just finishing up his work, one evening, preparatory to going home to supper, when the instrument on the chief-dispatcher's desk began to call. Allan, without really listening, heard the message: "Night man at Byers Junction reported sick. Send substitute." The chief-dispatcher clicked back "O. K.," and closed the key. Then he wheeled about in his chair and met Allan's eager eyes. "There's a job for you," he said, "if you want it." "Want it!" echoed Allan. "I certainly do!" "And if you think you can fill it," the chief added. "The work at Byers is pretty heavy." "I'll do my best," Allan promised. The chief looked at him for a moment longer, then nodded quickly and glanced at his watch. "You'll do," he said. "And you've only got thirty minutes. You'll have to catch Number Sixteen." "All right, sir; I'll catch it," said Allan, and he went down the steps two at a time. Mary Welsh was just spreading the cloth preparatory to getting supper when Allan raced up the steps leading from the street below and burst in at the door. "Why!" cried Mary. "What ails th' boy!" "Hooray!" yelled Allan, and seized her and danced around with her in his arms. "I'm going to be an op-e-ra-tor!" "Well, I'm sure," gasped Mary, releasing herself and reaching up to push the loosened hairpins back into place, "that ain't so wonderful. You'd ought t' been a oppeyrator long ago! A railroad ain't got no sense o' gratitude!" "There, there!" cried Allan. "The road's all right--and I've got to catch Number Sixteen--and I wonder if there's a crust of bread or a cold potato, or anything of that sort handy?" "Crust o' bread, indade!" snorted Mary, glancing at the clock. "You'll have your supper. Go an' git washed, an' I'll have it ready fer ye in a jiffy." "All right," said Allan, "but I warn you I'll be back in just a minute and a half."