“One of them evidently is on the way here. Some one whose initials are S. D.,” added Belden, glancing at the message. “If you can identify him and find Gus Dewitt——”
“I shall certainly do the latter,” Nick interposed. “But you are wrong in regard to the other.”
“How so?”
“S. D. does not, in all probability, refer to a man.”
“A woman?”
“No.”
“To what, then?”
“To a special-delivery letter,” said Nick confidently.
“Oh, by thunder!” Belden exclaimed. “That must be right, too. You have nailed every point in both of these messages.”
“And the next step, Belden, is to nail the special-delivery letter,” Nick declared. “It presumably is coming from Philadelphia, and most likely sent by this man Martin. Do you know whether a mail from Philadelphia has arrived here since ten this morning?”