"Mother had a headache and couldn't come," said Sally quietly. She must have been afraid that her father would ask other questions. It was quite natural that he should want to know who did come with her. So she went on rapidly. "But I thought I'd come just the same, so I did, and I went to your laboratory, but you'd just gone and I followed on after and I caught you just as you turned this corner, and now I would like to have you go down to the shops with me. I want to buy something for mother and Charlie. Will you go with me, father?" The professor did not ask any of the questions that Sally feared. Possibly he had as much fear of the answers as Sally had of the questions. So he asked none of the questions that one would think a father would ask of his little daughter in such circumstances. As Sally neared the end of her rapid speech, his eyes had narrowed. "So," he said slowly, "I gather from what you have left unsaid that your mother sent you after me." There was the faintest suspicion of a sneer in his voice, but he tried to speak lightly. As had happened many times before, he did not succeed. "She didn't," answered Sally, trying to be calm. Her eyes burned. "She didn't want me to come. I came on my own hook." "It might have been wiser, Sally," the professor observed judicially, "to do what your mother wished." Sally made no reply. She would have liked to ask him if he did--if he ever did what her mother wished. Sally saying nothing and seeming somewhat abashed, the professor found himself calmer. "So that course did not commend itself to your judgment? Didn't think it best to mind your mother. And you went to the laboratory and--who let you in?" he asked suddenly. "One of the cleaners." "Oh, one of the cleaners. A very frowzy lady in a faded black skirt and no waist worth mentioning, I presume." The professor seemed relieved. "And you went in, and didn't find me. Very natural. I was not there. And having made up your mind, from internal evidence, I presume, which way I had gone,--but who told you?--oh, never mind. It's quite immaterial. A very successful trail, Sally; or shall I say shadow? You must have the makings of a clever detective in you. I shouldn't have suspected it. Never in the world." The professor was quite calm by this time; rather pleased with himself, especially as he had chanced to remark the tears standing in his little daughter's eyes. "And I never suspected it!" he repeated. Then he laughed; but it was a mirthless laugh. If he had known how empty it would sound, the professor would never have done it. At his laugh, two of the aforesaid tears splashed on the sidewalk, in spite of Sally's efforts to prevent. The tears may not have been wholly on her own account. She may have felt some pity for her father's pitiful pretense. She bit her lip. "Will you go with me now, father?" she asked, as soon as she could trust herself to speak at all.