For reply Slim handed the bill to Joey, pointing with a grimy first finger at something on the reverse side.
It was an "O," scrawled in dull red ink.
"That would be an easy bill to identify," commented Palmer, uneasily, "wonder if this can be a trap?"
"Well, keep your suspicions to yourself for a while," counseled Joey; "we don't need to break it till we make sure."
CHAPTER XII.
WHAT HAPPENED TO ROY.
It was the next evening. Mortlake, sitting at his desk, looked up as a quick step sounded outside. The factory was in darkness as the men had gone home. Only a twilight dimness illuminated the little glass sanctum of the inventor and constructor of the Mortlake Aeroplane.
"Come in," said Mortlake, as the next instant a sharp, decisive knock sounded.