"The scoundrels have a long start of us!" exclaimed Jack. "We'll have to do the best we can."
"Better notify the police at once," suggested Tom. "We'll need their help."
"That's right," agreed his chum.
Their uniform was an open sesame to the police officials, and a detective was at once detailed to go with the boys to the restaurant. There, as might have been expected, there was no news. The spy, or whoever Potzfeldt's agent was, had been too clever for that. All that could be learned from a taxicab driver was that a lady and a girl, answering the descriptions of Bessie and her mother, had been met in front of the restaurant by a man.
The three, after a short talk, had driven off together in an automobile, and that was the last seen of them.
"But we'll get some trace," declared the detective. "It is hard to get in or out of Paris now without proper papers. And while, of course, this spy may have forged documents, there is a chance that we may intercept him and help your friends. Time is against us, but we will do our best."
Tom and Jack knew that. There was nothing else to do, and so, worried as they were, they went back to their comrades. Tom made some inquiries about his father, but, as he feared, no news had come.
As may be imagined Tom and Jack did not pass a very restful night. The Zeppelin raid had set their nerves on edge, as well as those of every one else, and it could not be told when the big gun might begin firing again. Then the fact of Mrs. Gleason and Bessie being missing, and not knowing in what danger they might be, added to the boys' anxiety.
They paid a late visit to the police, hoping for news, but the spy had not been apprehended. Then they hurried back to get a little rest before starting with their comrades of the air to search for the monster gun.
While these events were transpiring, the French army intelligence department had not been idle. The officials knew how vitally necessary it was, in order not to have the morale of the people of Paris weakened, to do something to find and silence the big guns. And first it was necessary to discover them.