"To the unaided eye," proceeded Ashton-Kirk, "the scrapings seemed but fragments of soil; but the lens showed me something more. Mixed with the earth were some whitish particles—these," and he indicated one of the little heaps of crumbled lime. "Association," and the investigator looked at his friend steadily, "is one of the commonest faculties of the mind. And as soon as I realized what the particles were, an idea took shape."
"An idea," said Bat, with a feeling of uneasiness growing upon him. "What sort of an idea?"
"True coincidence," said Ashton-Kirk, "is so infrequent an occurrence that I seldom consider it. The presence of the lime upon the cellar grating had no value, of course; but, as you know, a poker player will sometimes retain cards in his hand which are worth nothing in themselves, on the chance that he may draw certain others. And, once these are drawn, the heretofore valueless cards become of superlative importance."
There was a pause; Bat Scanlon knew the weight of this illustration, and sat in nervous expectation of what was to follow. "I had this idea in mind when I stepped on the scaffolding outside Miss Cavanaugh's window," proceeded Ashton-Kirk. "The maid said the workmen had not been on the job for some days, and so my search was not difficult. There were a great many footprints, unquestionably of the mechanics; but on top of these, plain and undisturbed, were the impressions of the 'creepers' which I had seen in the sod at 620 Duncan Street."
"You are sure?" said Bat Scanlon, in a flat, throaty voice. "There's no mistake?"
"Not any," replied the investigator, quietly.
Scanlon dropped the end of his cigar into a pewter bowl upon the table; then he lighted another and lay back in his chair, his brows drawn together in a heavy frown.
"All right," said he. "We'll let it go at that. There was a yegg of some kind scouting around Nora's house; and the same lad also took some observations of the place at Stanwick. We have that all settled. And now what does it mean?"
Ashton-Kirk smiled.
"I don't know," said he. "But suppose we try to find out." He took the telephone receiver from the hook and asked for police headquarters. In a few moments he had the person required.