They visualized the great, flat, low-lying stretches of southern Long Island and New Jersey; the abrupt bluffs of Long Island's northern coast by the shore of the Sound; the various watery arms that encircle the American metropolis, permitting ships to sail in every direction; the majestic Hudson leading straight north through a wonderful country of rocks and hills, the impressive Palisades flanking its western bank with their towering perpendicular walls of stone; and the rocky, rolling country lying west of them, interspersed with streams and swamps and woodlands and open fields and clustered villages. And when they had finished their study of the maps, they knew more about the topography of the country they had studied, its roads and paths and groves and elevations and other physical characteristics, than half the people who lived in the region. So they were prepared, if need be, to find their way about with little difficulty. And it was well they were so prepared. In the dangerous days to come they were to need all this knowledge.
When they had studied the maps to their hearts' content—and each of the four boys again and again examined them—Captain Hardy folded the maps and thrust them into a waterproof cover. They made a neat little packet like a thin book.
"You will be interested to learn what the secret service has found out," said Captain Hardy, as he stowed the maps in his pocket. "When I left here, I reported immediately to the man in charge of this particular investigation. Our discovery seems to me so important that I ventured to ask why the secret service men didn't take the case up themselves, as they would no doubt get along much faster than we possibly can. For it seems to me message sending ought to be stopped at once. The agent said that all this was true, but that the secret service was so crowded with work it had to take up the most important matters first."
"Most important matters!" cried Roy, in indignation. "Doesn't the secret service consider the guarding of our troops important?"
"Yes, Roy. But whether the Germans know exactly when our ships leave or not, their submarines will be waiting for them and our destroyers will always be guarding the transports. But here in New York German spies are trying to create riots, to blow up buildings, to burn factories. They destroyed almost a million bushels of wheat in one fire recently. So you see that the secret service first must watch the enemies that are trying to destroy our greatest city. Our secret service isn't one-quarter as large as it should be. That is the fault of Congress. But meantime it is doing wonderful work, and it is a great privilege to be able to assist in that work."
"But what have they found out about this job?" demanded Roy.
"You're like a hound on a keen scent, Roy," said their leader. "Nothing ever takes you away from your objective. Well, this is what they've found. It seems that they have been keeping a record of the grocer's telephone messages, as well as those from the 'hawk's nest' down below. Every time transports sail, some one in Hoboken calls up this grocer and says, 'I have some sugar on the way. Do you want any?' And the grocer replies, 'Yes. How many barrels can you let me have?' And the man in Hoboken gives the number. That number corresponds with the number of transports about to sail. So you see how the grocer knows when to send his boy for the wireless messages. But before he sends him, he always telephones to the 'hawk's nest' and says, 'I have some sugar coming and can let you have five pounds to-day. Do you want it?' And the number of pounds he offers is the same as the number of ships that are to sail. So the spy below us knows what to look for. And I suppose the man in Hoboken also telephones the automobile driver when to come for the dollars."
"Who is this man in Hoboken that does the telephoning?" demanded Roy, when Captain Hardy had done speaking.
"Ah! That they don't know. He has always called up from a different place and has gotten away before the secret service could spot him. But the agent assures me that they'll have him soon. He always telephones from a station close to the piers where the transports load. The next time he calls for the grocer, the telephone operator is going to delay him while she notifies a secret service agent posted near by with a motor-cycle. So they'll spot him and trail him.
"And that reminds me," continued Captain Hardy, after a pause, "that we're to do a little motor-cycle work ourselves, and that Henry has been selected for the job because he is familiar with motor-cycles."