Central City. It was Roy's keen eye that caught sight of the great maps of the world high up on the walls. The crowds of people coming and going hardly seemed like crowds, so vast was the structure. With reluctant feet the four boys pushed on. But when they had mounted the steps to the arcade and caught sight of the illuminated transparencies showing scenes along the railway's path, they came to a dead stop. For Willie Brown, with his almost uncanny eye for landscapes, at once declared that a certain picture represented a mountain scene not twenty-five miles from Central City; and when the others appealed to Captain Hardy, the latter confirmed Willie's statement.

When the four lads reached the sidewalk they were almost distracted. Thousands of people were hurrying along, passing in endless throngs up and down the street. Never had the boys from Central City seen people in such a rush.

"What's the hurry?" demanded Roy. "Why does everybody walk so fast? What's up?"

"Nothing," replied Captain Hardy, with a smile. "That's just the New York gait. Everybody walks fast here, and does everything else fast; and if you boys want to make a reputation in New York you'll have to hustle some. But I don't want you to make that kind of a reputation," he continued, hastily yanking Willie Brown from in front of a passing motor-car. "You will have to keep your eyes open here."

And indeed they had to. Motor-cars were rushing about as numerous as flies in August. Trolley-cars followed one another up and down Seventh Avenue in endless processions. Wagons and trucks stretched along the highway in slow-moving lines as far as the eye could see. Bells were ringing, whistles tooting, horns blowing, motor-cars honking, newsies shouting. The grinding of car-wheels, the rattle of carts, the clatter of hoofs on the asphalt, the shuffling of feet on the sidewalk, and a thousand other noises combined to make an indescribable and confusing roar. The noise and bustle were bewildering.

"I guess mother was right," thought Henry. "It would be mighty easy to get lost here. The wireless patrol will have to look sharp or the police will be called upon to find it."

And indeed there were so many distracting things that the four spy hunters found it difficult not to get lost. At every step something new and unfamiliar claimed their attention and caused them to pause and look about.

Captain Hardy let his charges go at their own gait. He paused when they wanted to look at something, took sharp care of them at crossings, and told them how to cross the streets so as to avoid accidents. And ever he kept his eye on them to see that none of the four became separated from the group. It pleased him to note how quickly they learned to avoid the traffic and dodge difficulties. Their training in observation had not been in vain.

To Herald Square the captain led his party. There, in a little eddy of sidewalk traffic, he drew them together.

"The streets that run lengthwise of the island," he said, "are called avenues, and the one before you is Sixth Avenue. The station we just left faces on Seventh Avenue. The cross streets are numbered, and the one we are on is Thirty-fourth Street. Broadway comes up the island on a long diagonal. Right here where Broadway, Thirty-fourth Street, and Sixth Avenue intersect, is one of the busiest corners in the city. Overhead are two elevated railway tracks. On the ground are six street-car tracks, crossing one another. Under the surface are two subway tracks. So you have three layers of people passing and repassing above or below one another. I want you to remember what I have said as to the arrangement of the thoroughfares—avenues run north and south, streets east and west. If you get that thought in your mind, you won't go very far out of your way.

"And there is one thing more to remember. In some cities, such as Philadelphia, the street numbers run 100 to each block. Here the houses are numbered consecutively, and you can't tell by a number where a house is. But if you should need to know, go to the nearest drug store. Every New York drug store has a city directory. And in the back of the directory you will find a table that will show you approximately where to find the street number you want. Don't forget. If you are to do effective work, you must become so familiar with New York that you can find your way around as readily as you can in Central City. Sometimes it may be necessary for you to go from place to place in the shortest possible time and you must know not only how to get there, but also how to take advantage of short cuts. We'll get some maps after a time and study them."

His young companions plied their leader with a thousand questions. They wanted to know the names of all the big buildings in sight. They had all heard of the Waldorf-Astoria Hotel and they gazed up Thirty-fourth Street at this well-known hostelry with much curiosity. They had heard of the Times Building and were eager to see it.

"We can't spend much time sightseeing just now," said Captain Hardy. "We must get into touch with the police and the secret service people and get our instructions. Then we will take a day or two, if possible, and see something of the town. It is most important for you to become well acquainted with it at once. But I guess we can take time to slip up to Times Square. It's only eight blocks up Broadway. Now I want you boys to see everything you can as we go along, and to try to remember all that you see. Wherever you go you must remember that you are in New York to detect German spies and presumably to run down German wireless outfits. We don't know where they are. We may be looking at one this very instant. So keep your eyes open. If you see anything that resembles a wireless outfit, or that might be used for sending messages, take careful note of it. And keep your ears open for suspicious conversations. Because you are boys, people will be less careful in their talk when you are present than they would be with older people about. The more youthful and unsophisticated you can make yourselves appear, the better it will be for your purpose."

Slowly the little party made its way up Broadway. By degrees the lads became accustomed to the roar of the traffic and the rush of pedestrians. At Times Square they paused for a look at the great newspaper building that gives the place its name, and at the great hotels rising on every side. Then they passed down a long flight of steps and found themselves in a low, vaulted, underground subway station.

"Makes you think of the dugouts on the firing-line in France," suggested the quick-witted Roy.

An instant later a train thundered up to the platform and the boys boarded it. A short ride and a short walk took them to Police Headquarters.

Captain Hardy sent his card to the Police Commissioner, with the request for a brief interview. A few moments later he had presented his credentials and introduced his companions, and four delighted boys found themselves blushingly shaking hands with New York's famous chief of police, Arthur Woods. Briefly Captain Hardy stated the purpose of his visit and related the story of the capture of the Elk City dynamiters.

"I recall the incident distinctly," said the Commissioner. "The newspapers were full of it. And I recall that when I read the story I wished I had as accomplished and clever a squad of boys to help me with some of my hard problems."

The four boys flushed with happiness. But they were too much embarrassed to make any reply.

"Captain Hardy," said the Commissioner, "what is your plan of action?"

"We have none as yet. We are to work under the direction of the secret service. But we have not seen Chief Flynn yet. The boys just arrived."

"Let me make one suggestion to you," said the Commissioner, turning again to the boys. "Before you attempt to do any detective work make yourselves familiar with the city. Get some maps and study them until you know every street and alley. Take your maps and go over the city on foot. Put several days in