"Not necessarily," replied Roper, dryly; "but this, that if Vassalla knew she was on board that night, he also knew she committed the murder, and would therefore have a power over her; but her determination to stop the marriage shows that she must have some power over him; so that either she is innocent, or he committed the murder himself, and she can force him by fear of exposure to do what she wants." "And which of these theories do you think is right?" asked Foster. "I am doubtful," said the detective, becoming a little agitated; "but I--I have a third theory." "Yes?" said Ronald, in a quiet tone, looking strangely at the detective. Roper arose to his feet, and took a walk up and down the room for a minute, then turned to the young men, who were puzzled by his curious manner. "Of course, it's only a theory," said Roper, nervously; "but--but--I can only tell you what I think." "Tell us, in heaven's name!" cried Foster, rising. "Then I think Miss Carmela Cotoner committed the crime." "What?" Ronald sprang to his feet, and made a spring at the detective, but Foster caught him and held him back. "Be quiet Ronald, be quiet," he said, firmly. "A lie, a cursed, black lie," panted Ronald, glaring at the detective, who stood quietly looking at him. "What proof, what pro-- D--n you, sir, where is your proof?" Roper took out of his pocket-book the yellow scrap of paper given by Mrs. Taunton, and the fragment of a letter written by Carmela to her sister. "I obtained these through Mrs. Dexter," he said, quietly placing them on the table; "look!" Ronald looked for a moment, then reeled back into Foster's arms. "My God! my God!" he sobbed. "My God!" The handwritings were identical in every particular. Foster went to a cupboard and got Ronald a glass of brandy, which he forced him to swallow; then, leaving the young man in the chair, with his face buried in his hands, he sat down at his own table, and began to speak to Foster. "How did you make this discovery?" he asked, quietly. "I remembered in Mr. Monteith's story," said Roper, "that both sisters loved the husband, and I wondered if it were not possible that the younger might commit the crime quite as well as the elder, though, I confess to you, I had no grounds for my suspicion. As I told you in my letter, I obtained a specimen of Mrs. Verschoyle's handwriting, and found, by comparison with this paper"--laying his hand on the yellow sheet--"that, though there was a similarity, there was also a slight difference. This began to confirm my theory, and by the kind aid of Mrs. Dexter, I obtained this letter of Miss Cotoner's, by which you will see they correspond in every particular." At this moment Ronald arose from his seat, and staggering to the table, produced from his pocket-book the note written to him by Carmela before the "Neptune" reached Gibraltar. Laying this down by the other papers, with a shaking hand, at the first glance it could be seen the handwritings were identical.