"I never realized before," said Jane, "how many Germans there were all about us."
"In an effort to locate this particular band of naval spies," continued Mr. Fleck, "we have combed the apartment houses and residences along the Drive. Three places in particular are under suspicion. The apartment of the Hoffs is one of these places. They moved in there thirty days after this country went to war. Ordinarily, where the occupants of an apartment are under suspicion, we take the superintendent of the building partly into our confidence and plant operatives in the house, or else we hire an apartment in the same building. In this case neither course is practicable. The superintendent of your building is a German-American and we dare not trust him, and there is no vacant apartment that we can rent. We have been watching the Hoffs from the outside as best we could. Carter, who has had charge of the shadowing, accidentally happened to overhear you give your address. He had procured a list of the tenants and remembered the location of your apartment. It struck him at once that you would be a valuable ally if you would consent to work with us."
"What is it that you wish me to do?" asked Jane wonderingly. "You'll have to tell me how to go about it."
"All a good detective needs," said Mr. Fleck, "is, let us say, three things--observation, addition and common sense. You must observe everything closely, be able to put two and two together and use your common sense. Do you know the Hoffs by sight?"
"Only by sight."
"They live in the next apartment on your floor, do they not?"
"Yes. Young Mr. Hoff's bedroom is the room next to mine."
"Good," cried Mr. Fleck. "Can you hear anything from the next apartment, any conversations?"
"No, only muffled sounds."
"The windows overlook the river and the transports, do they not?"
"Yes, the windows of Mr. Hoff's bedroom and the room next. Their apartment is a duplicate of ours."
Mr. Fleck sprang up and crossed to the big safe. Opening an inner drawer he took out a small metal disk and handed it to her. Jane looked at it curiously. It bore no wording save the inscription "K-19."
"That," said Mr. Fleck, "is the only thing I can give you in the way of credentials. Keep it somewhere safely concealed about your clothing and never exhibit it except in case of extreme necessity. If ever you are in peril any police officer will recognize it at once and will promptly give you all the assistance possible."
"But," protested the girl, "I don't know yet what I am to do."
"For the present I am trusting to your resourcefulness to make opportunities to help us. We are watching the house closely from the outside. Carter will identify you to the other operatives. Once a day I will expect you to call me up, not from your home but from a public 'phone. Here is my number. Say 'this is Miss Jones speaking,' and I will know who it is. I can communicate with you by note without arousing suspicion?"
"Oh, yes, certainly."
"If at any time I have to call you on the 'phone, or if any of the other operatives want to communicate with you the password will be 'I am speaking for Miss Jones.'"
"Isn't that exciting--a secret password," cried Jane enthusiastically.
"If you can manage it without compromising yourself too seriously, I wish you would make the young man's acquaintance."
"That will be simple," said Jane, remembering the admiring way in which he had raised his cup in her direction as she left the hotel.
"If possible find out who their visitors are in the apartment and keep your eyes open for any sort of signalling to the transports. If ever there is an opportunity to get hold of notes or mail delivered to either of them, don't hesitate to steam it open and copy it."
"Must I?" said Jane. "That hardly seems right or fair."
"Of course it's right," cried Mr. Fleck warmly. "Think of the lives of our soldiers that are at stake. The devilish ingenuity of these German spies must be thwarted at all costs. They seem to be able to discover every detail of our plans. Only two days ago one of our transports was thoroughly inspected from stem to stern. Two hours later twenty-six hundred soldiers were put aboard her on their way to France. Just by accident, as they were about to sail, a time-bomb was discovered in the coal bunkers, a bomb that would have sent them all to kingdom come."
"How terrible!"
"Somebody aboard is a traitor. Somebody knew when that inspection was made. Somebody put that bomb in place afterward. That shows you the kind of enemies we are fighting."
Jane shuddered. She was thinking of the sailing of another transport, the one that had carried her brother to France.
"Anything seems right after that," she said simply.
"Yes," said Mr. Fleck, "there is only one effective way to fight those spying devils. We must stop at nothing. They stop at nothing--not even murder--to gain their ends."
"I know that," said Jane hastily. "I saw something myself you ought to know about."
As briefly as she could she described the scene she had witnessed in the early morning hours from her bedroom window, the man following the younger Hoff, Hoff's discovery and pursuit of him around the corner and of his return alone.
"And in the morning," she concluded, "they found a man's body in the side street. He had a bullet through his heart. There was a revolver in his hand. The newspapers said that the police and the coroner were satisfied that it was a suicide. I caught a glimpse of Mr. Hoff's face when he came back from around that corner. It was all convulsed with hate, the most terrible expression I ever saw. I'm almost certain he murdered that man. I'm sure it wasn't a suicide."
"I'm sure, too, that it was no suicide," said Mr. Fleck gravely. "The man who was found there was one of my men, K-19, the man whose badge I have just given you. He had been detailed to shadow the Hoffs."
CHAPTER IV
THE CLUE IN THE BOOK
Subway passengers sitting opposite Jane Strong as she rode up-town from Mr. Fleck's office, if they observed her at all--and most of them did--saw only a slim, good-looking young girl, dressed in a chic tailormade suit, crowned with a dashing Paris hat tilted at the proper angle to display best the sheen of her black, black hair, which after the prevailing fashion was pulled forward becomingly over her ears. Outwardly Jane was unchanged, but within her nerves were all atingle at the thought of the tremendous and fascinating responsibility so unexpectedly thrust upon her. Her mind, too, was aflame with patriotic ardor, but coupled with these new sensations was a persisting sense of dread, an intangible, unforgettable feeling of horror that kept cropping up every time her fingers touched the little metal disk in her purse.
The man who had carried it yesterday, the other "K-19" who had undertaken to shadow those people next door, now lay dead with a bullet through his heart. Was there, she wondered, a similar peril confronting her? Would her life be in danger, too? Was that the reason Mr. Fleck had told her of her predecessor's fate--to warn her how desperate were the men against whom she was to match her wits? Yet no sense