“Wait!” motioned Vaux to Miss Erith.  He went to the stairs, listened to the progress of agent and prey, heard the street-door clash, then hastened back to the lighted dining-room, pulling the “Perfect Cook-Book” from his pocket.

“I found that in the kitchenette,” he remarked, laying it before her on the table.  “Maybe that’s the key?”

“A cook-book!” She smiled, opened it.  “Why—­why, it’s a dictionary!” she exclaimed excitedly.

“A dictionary!”

“Yes!  Look!  Stormonth’s English Dictionary!”

“By ginger!” he said.  “I believe it’s the code-book!  Where is your cipher letter, Miss Erith!”

The girl produced it with hands that trembled a trifle, spread it out under the light.  Then she drew from her pocket a little pad and a pencil.

“Quick,” she said, “look for page 17!”

“Yes, I have it!”

“First column!”

“Yes.”

“Now try the twentieth word from the top!”

He counted downward very carefully.

“It is the word ‘anagraph,’” he said; and she wrote it down.

“Also, we had better try the twentieth word counting from the bottom of the page up,” she said.  “It might possibly be that.”

“The twentieth word, counting from the bottom of the column upward, is the word ‘an,’” he said.  She wrote it.

“Now,” she continued, “try page 15, second column, third word from top!”

“‘Ambrosia’ is the word.”

“Try the third word from the bottom.”

“‘American.’”

She pointed to the four words which she had written.  Counting from the top of the page downward the first two words were “Anagraph ambrosia.”  But counting from the bottom upward the two words formed the phrase:  “An American.”

“Try page 730, first column, seventh word from the bottom,” she said, controlling her excitement with an effort.

“The word is ‘who.’”

“Page 212, second column, first word!”

“‘For.’”

“Page 507, first column, seventh word!”

“‘Reasons.’”

“We have the key!” she exclaimed.  “Look at what I’ve written!—­’An American who for reasons!’ And here, in the cipher letter, it goes on—­’of the most’—­Do you see?”

“It certainly looks like the key,” he said.  “But we’d better try another word or two.”

“Try page 717, first column, ninth word.”

“The word is ‘vital.’”

“Page 274, second column, second word.”

“‘Importance!’”

“It is the key!  Here is what I have written:  ’An American who for reasons, of the most vital importance!’ Quick.  We don’t want a Secret Service man to find us here, Mr. Vaux!  He’d object to our removing this book from Lauffer’s apartment.  Put it into your pocket and run!” And the pretty Miss Erith turned and took to her heels with Vaux after her.

Through the disordered apartment and down the stairs they sped, out into the icy darkness and around the corner, where her car stood, engine running, and a blanket over the hood.