“A joke?” she repeated.  “Do explain, I’m dying to know all about it.”

“It wasn’t half as difficult a job as one might imagine, you know.  Our censor chaps at home have got to be quite expert at reading letters, invisible ink and all that sort of thing.  Hoff for months had been sending cipher messages to the war office in Berlin.  He kept urging them to act on his all-wonderful plan for blowing up New York.  They decided finally to try it and notified old Otto they were sending over an officer to supervise the job.”

“What became of him?  The officer they sent over?”

“Our people picked him off a Scandinavian boat and locked him up.  They took his papers and turned them over to me.  Clever, wasn’t it?”

“And you took his name and his papers and came here in his place?  Oh, that was a brave, brave thing to do.”

“I wouldn’t say that,” said Seymour modestly.  “I fancy I look a bit like the chap, and I speak the language perfectly.”

“But it was such a terrible risk to take,” cried Jane with a shudder.  “Suppose they’d found you out?”

“No danger of that,” laughed Frederic.  “Old Otto never had seen the chap who was coming.  His real nephew, Frederic Hoff, whose American birth certificate was used, died years ago.  Besides I had the German officer’s papers and knew just what his instructions were.  The worst of it was when old Otto insisted every night on toasting the Kaiser, and when he kept trying to get me mixed up in his dirty schemes.  I had to go through with the former once in a while, but on the latter, I—­how do you Americans say it—­just stalled along.  My orders were to land him only on the big thing—­his wonder-workers.”

“But how did you explain to him that British uniform?”

“Now that was really an idea.  The old fellow was getting a bit cross and suspicious with me because he thought I wasn’t doing enough while they were getting his ‘wonder-workers’ ready.  At one time he was so distrustful of me that he had me followed.”

“Oh, yes, I know,” said Jane quickly.  With a thrill she remembered the scene she had witnessed from her window the night K-19, her predecessor on Chief Fleck’s staff, had been murdered.  In her relief at discovering that Frederic was no German spy, she had forgotten that for weeks and weeks she had all but believed him guilty of murder.  Now, something told her, surely and confidently, that he could explain it all.

“I saw you from my window one night before I met you,” she went on.  “A man was following you, and you chased him around the corner.”

“I remember that,” he said; “the poor chap was found dead the next morning.  Old Otto killed him.  The man had been following me, and I had imagined that he was one of old Otto’s spies and knocked him down.  I couldn’t find anything on him to indicate who he was, so just as he was beginning to revive I left him and came on home.  It seems old Otto had been watching him trail me.  He followed along and shot the man.  He gleefully told me about it the next day, the hound.  I ought to have given him over to the police, but that would have upset our plans.”