“You see,” she continued, opening the portfolio, “here is my copy of this wretched cipher letter.  I have transferred it to one sheet.  It’s nothing but a string of Arabic numbers interspersed with meaningless words.  These numbers most probably represent, in the order in which they are written, first the number of the page of some book, then the line on which the word is to be found—­say, the tenth line from the top, or maybe from the bottom—­and then the position of the word—­second from the left or perhaps from the right.”

“It’s utterly impossible to solve that unless you have the book,” he remarked; “therefore, why speculate, Miss Erith?”

“I’m going to try to find the book.”

“How?”

“By breaking into the shop of Herman Lauffer.”

“House-breaking?  Robbery?”

“Yes.”

Vaux smiled incredulously: 

“Granted that you get into Lauffer’s shop without being arrested, what then?”

“I shall have this cipher with me.  There are not likely to be many books in the shop of a gilder and maker of picture frames.  I shall, by referring to this letter, search what books I find there for a single coherent sentence.  When I discover such a sentence I shall know that I have the right book.”

The young man smoked reflectively and gazed into the burning coals.

“So you propose to break into his shop to-night and steal the book?”

“There seems to be nothing else to do, Mr. Vaux.”

“Of course,” he remarked sarcastically, “we could turn this matter over to the proper authorities—­”

“I won’t!  Please don’t!”

“Why not?”

“Because I have concluded that it is part of our work.  And I’ve begun already.  I went to see Lauffer.  I took a photograph to be framed.”

“What does he look like?”

“A mink—­an otter—­one of those sharp-muzzled little animals!—­Two tiny eyes, rather close together, a long nose that wrinkles when he talks, as though he were sniffing at you; a ragged, black moustache, like the furry muzzle-bristles of some wild thing—­that is a sketch of Herman Lauffer.”

“A pretty man,” commented Vaux, much amused.

“He’s little and fat of abdomen, but he looks powerful.”

“Prettier and prettier!”

They both laughed.  A pleasant steam arose from the tall glass at his elbow.

“Well,” she said, “I have to change my gown—­”

“Good Lord!  Are we going now?” he remonstrated.

“Yes.  I don’t believe there will be a soul on the streets.”

“But I don’t wish to go at all,” he explained.  “I’m very happy here, discussing things.”

“I know it.  But you wouldn’t let me go all alone, would you, Mr. Vaux?”

“I don’t want you to go anywhere.”

“But I’m going!”

“Here’s where I perish,” groaned Vaux, rising as the girl passed him with her pretty, humorous smile, moving lithely, swiftly as some graceful wild thing passing confidently through its own domain.