“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 of fear that projected itself into her busy brain as she cogitated over the task before her held her back.  If anything she was rather thrilled at the prospect of meeting actual danger.  What bothered her most was how she could best go about aiding Mr. Fleck and his men in their work.