“But how’ll you get their door open?”

Dean smilingly drew forth a key.

“I borrowed the superintendent’s bunch last night, pretending I had lost the key to my locker in the basement.  I knew he had a master-key that unlocks all the apartment doors, and there was no trouble in picking it out.  I had some wax in my hand and made an impression of it right under his nose.”

“How clever,” cried Jane, “but suppose the Hoffs do not go off to-morrow.  What will we do then?”

“You are taking tea with young Hoff this afternoon, aren’t you?”

“Yes,” said Jane, “that is, he asked me to.  I am to meet him at the Biltmore at five.”

“When you’re with him propose doing something together to-morrow afternoon.  See what he says.”

“That’s an excellent idea.  I’ll ask him to go to the matinee with me.”

“That will do splendidly.  Has he been with that navy officer lately?”

“Not since Sunday, to my knowledge.  I wonder if old Mr. Hoff has left any more cipher messages at the bookshop?”

“No,” said Dean, “he hasn’t.  The place has been constantly watched, but he hasn’t been near it since that first day.”

“I’m afraid,” sighed Jane despondently, “I betrayed the fact that we were watching them to the nephew.  He overheard me talking to Carter about the ‘fifth book,’ and of course he knew what it meant.  I’m certain the old man is still reporting about our transports.  Every day I can hear some one telephoning to him.  He waits for the message, and then he goes out.”

“He certainly is expert in eluding shadowers,” admitted Dean.  “Every day he has been followed, but always he manages to give the operatives the slip.  He must know he is being watched.”

“I’m anxious to know what the nephew will say to me to-day,” said Jane.  “I know he knows what I am doing.  He looks at me in such an amusedly superior way every time he sees me.”

“Be careful about trying to pump him,” cautioned Dean.  “He strikes me as by far the more intelligent of the two.  It would not surprise me in the least if he were not old Hoff’s nephew at all, but really his superior, sent over especially by Wilhelmstrasse to take charge of the plotters.  He doesn’t in the least resemble old Hoff.”

“No indeed, he doesn’t,” admitted Jane.  “He certainly is clever, too.  We haven’t learned a single thing that incriminates him, have we?”

“Nothing definite, yet everything taken together looks damaging enough.  Here is a young German of military age and appearance, who arrived from Sweden just before we went into the war.  He has plenty of money and spends his time idling about New York, in frequent communication with at least one navy officer.  He selects a home overlooking the river from which our soldiers are departing for France.  You yourself saw him pursuing K-19—­the other K-19—­who a few hours afterward was found murdered.”