“Just across the street,” said Jane, entering into the spirit of the masked conversation with interest.  “I was looking at a fine book over there a few minutes ago.  You’ll find it on the second shelf—­the fifth book from the end, on the north side of the store.”

“I’ll remember that,” said Carter, repeating, “the fifth book on the second shelf.”

“That’s right,” said Jane, as they left the drug-store together.

“Which way did the old man go?” asked Carter.

“Down Broadway—­toward home,” she replied.  “I wanted to follow him, but it seemed more important to stay here and watch to see if any one came for the message he left there in the book.”

“You did just right, and the Chief is tickled to death.  He wants to see you right away.  You have a copy of the message, haven’t you?”

“Yes, do you wish to see it?”

“No, but he does.  Has anybody entered the store since you were there?”

“Nobody, that is no one but a couple of girls.”

“What did they look like?  Describe them.”

“Why,” Jane faltered, “I did not really notice.  I was not looking for girls.  I was watching to see that no other men entered the store.”

Carter shook his head.

“You ought to have spotted them, too.  You never can tell who the Germans will employ.  They have women spies, too,—­clever ones.”

“I never thought of their using girls,” protested Jane.

“Humph,” snapped Carter, “ain’t we using you?  Ain’t one of our best little operatives right this minute working in a nursegirl’s garb pulling a baby carriage with a baby in it up and down Riverside Drive?  Well, it can’t be helped.  You’d better beat it down-town to the Chief right away.”

“I’ll take a subway express,” said Jane, feeling somewhat crestfallen at his implied suggestion of failure.

Twenty-five minutes later found her once more in Mr. Fleck’s office.  Thrilling with the excitement of it all she told him in detail how she had followed old Hoff and of his peculiar actions in the bookstore.

“And here,” she said, presenting the postcard, “is an exact copy of the cipher message he left there.  I copied every figure, in the columns, just as they were set down.  I don’t suppose though you’ll be able to make head or tail out of it.  I know I can’t.”

“Don’t be too sure of that,” smiled Chief Fleck, as he took the card.  “When you get used to codes, most of them identify themselves at the first glance—­at least they tell what kind of a code it is.  That’s one thing about the Germans that makes their spy work clumsy at times.  They are so methodical that they commit everything to writing.  Now the most important things I know are right in here”—­he tapped his head.  “Every once in a while they ransack my rooms, but they never find anything worth while.  Now this code”—­he was studying the card intently—­“seems to be one of a sort that our friends from Wilhelmstrasse are ridiculously fond of using.  It is manifestly a book code.”