“Explain the significance of that, won’t you?” asked Granniss. “Or are you one of those secretive detectives?”
“Not at all. That dust is, to my mind, from the shoe of the man who tried to rob this safe last night, thinking that money was in it. Now, I admit, Mr Granniss, that you knew, or thought you did, that the money was there; you knew the combination; you are quite strong enough to have strangled a woman who surprised you at your job; yet I know you didn’t have anything to do with the attempted robbery, because——”
“Because you love Betty!” Zizi said, softly, her eyes shining with sympathy and understanding. “Right you are, Wise, go on.”
“Also, because,” Wise went on, “because, I’m sure that is the footprint of the would-be burglar, and while the footprint as a print is too indistinct to be a clue to the man who made it, yet the dust that forms the print is indicative. It is a fine dust made up of particles of cement. I mean such dust as would adhere to a shoe that had traversed a cement floor, and, more likely an imperfect cement floor.”
“That means the cellar!” Rodney cried; “I’ve been down there a lot of late, poking around for that everlasting secret passage, and there’s a lot of loose cement.”
Wise gave him a quick glance, but his enthusiasm was so genuine, that the detective dismissed a sudden qualm of suspicion.
“Slip down and get me a sample, will you?” he said, and Granniss went at once.
“Big case, Zizi,” Wise said, as the two were left alone.
But he spoke heavily, almost despairingly, and with no show of his usual exultant interest in a big case.
“Yes, but,” the black eyes turned hopefully to his own, “there are tangible clues. And those of Betty’s can wait. Do you chase those that have to do with Martha first.”