It was with mixed feelings that Fairfield yielded at last to Foyle's arguments and returned to see Eileen Meredith. To his consent he had attached the condition that he was to be allowed to use his own judgment as to how much of the interview he should communicate to the detective, and with this Foyle had to be content. The baronet found the girl waiting for him, her face alight with eagerness. She was in her own boudoir, luxuriously ensconced in a big arm-chair, and she smiled brightly at him--such a smile as he had not seen since before the murder. He obeyed her invitation to sit down. "You wanted to see me alone," he said. She nodded. "Yes, I want to know if we are allies--or enemies. I know I have treated you abominably, but I was driven half mad by the thought that Bob was dead. Now we are working together--are we not?" He made a little gesture with his hands, helplessly as one at a loss. "In so far as we both wish to get Grell out of his difficulty--and I wish I knew what that was--yes," he replied. "I don't believe him to be a murderer, but why does he remain in hiding? He is not the sort of man to do foolish things, and that is foolish on the face of it. He has some strong reason for being out of the way. Can you explain?" She pulled her chair closer to him, and laid one slim hand on his. "I cannot explain--I can only trust. He looked to us to help him. I know that he wants money, for he sent a friend to tell me. I had none, but I gave her my jewels. Detectives were watching her, and they, with the connivance of my father, took them from her. Now, you, his most intimate friend, must help him. He has given you the key to the cipher which will appear, and then, I suppose, he will tell you how to get it to him." She had apparently taken it for granted that the baronet was with her in whole-souled devotion to her lover. His fingers beat a tattoo on his knee. "So that advertisement was the key to a cipher? Do you know when I shall get a message?" "I shall get one to-morrow. You--who knows?" "Then you can tell me how to read it?" 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."