remark, drawing the revolver, placing it against his breast, and pulling the trigger before he had time to recover from his horrified astonishment. He moved instinctively, though, just as the weapon exploded—which would account for the diagonal course of the bullet. Then Ada returned quickly to her own room and got into bed. Thus was another chapter written in the Greene tragedy."
"Did it strike you as strange," asked Markham, "that Von Blon was not at his office during the commission of either of the crimes?"
"At first—yes. But, after all, there was nothing unusual in the fact that a doctor should have been out at that time of night."
"It's easy enough to see how Ada got rid of Julia and Chester," grumbled Heath. "But what stops me is how she murdered Rex."
"Really, y' know, Sergeant," returned Vance, "that trick of hers shouldn't cause you any perplexity. I'll never forgive myself for not having guessed it long ago,—Ada certainly gave us enough clews to work on. But, before I describe it to you, let me recall a certain architectural detail of the Greene mansion. There is a Tudor fireplace, with carved wooden panels, in Ada's room, and another fireplace—a duplicate of Ada's—in Rex's room; and these two fireplaces are back to back on the same wall. The Greene house, as you know, is very old, and at some time in the past—perhaps when the fireplaces were built—an aperture was made between the two rooms, running from one of the panels in Ada's mantel to the corresponding panel in Rex's mantel. This miniature tunnel is about six inches square—
