She hesitated a moment, finger on chin. Then, animated by a quick resolve, she moved to a little inlaid desk and unlocked a drawer. She returned with a piece of paper in her hand.
"What was the number mentioned in your advertisement?"
"2315."
For a little the only sound in the room was the scratching of pencil on paper. At last she finished, and handed the result to him. He wrinkled his brows as he studied it.
| THIS | IS | THE | KEY |
| 2315 | 23 | 152 | 315 |
| VKJX | KV | UMG | NFD |
"The bottom line is the top one turned into cipher," she explained. "The middle line is the key number. In the first word you take the second letter from T, the third from H, the first from I, and so on. It is a cipher that cannot be unravelled without the key number. H becomes K once and M once."
"I see." The simplicity of it at once dawned on him. "That was what Foyle meant when he said that some ciphers could not be solved by the recurring E," he said unthinkingly.
She had risen and flung away from him in quick revulsion. One glance at her face told him what he had done.
"You spy!" There was stinging scorn in her tone. "You have talked it over with Foyle, and that man knows all. You are here to worm out what I know in order to betray your friend. Oh, don't trouble to lie,"—as he would have spoken,—"I can see your object. And I nearly fell into the trap."
The man was not without dignity, as he stood a little white but steady. "You may call me what you like," he said in a low voice. "Spy, if you will. Believe me or not, I have acted for the best, for you and for Grell. You once called me a murderer—with what justification you now know. Are you so ready to judge hastily again?"