Laura could not quite understand his meaning, since it never struck her that he meant to incriminate her in the matter. She took no notice, being anxious to learn what Derrick thought. "What is your theory on existing facts?" she asked coldly. Derrick reflected. "I hardly know what to say. Let us suppose that the woman admitted herself into the house. How she got the latch-key I am not prepared to say. She came to meet some one--possibly the two people who killed her." "The two people?" interrupted Laura abruptly. "There was the young man who kept Mulligan in talk," explained the officer, "and the one who presumably killed her. Let us suppose, for the sake of argument, that this woman met these two men. Seeing a policeman at the gate, Number One goes out to lure him away. Left alone with Number Two, the woman sits at the piano to sing. On the music-stand is 'Kathleen Mavourneen.' She knows that song and sings it. The assassin, standing behind her, watches his opportunity and stabs her. Then he goes." "You forget that the song was being sung, according to your own account, before Number One left the gate with the policeman." "Certainly. But the woman might have begun to sing immediately after Number One left." "Before," insisted Laura. "The policeman listened while Number One was in the room. It was the song that made him stop. I am only going by what you told me. Your theory doesn't fit together." Derrick frowned. "It is hard to put the pieces of the puzzle together, Miss Mason. Only in detective fiction does the heaven-born genius put this and that together in a flash. I--a mere mortal--am groping in the dark. I may discuss a hundred theories before I hit on the right solution. Nothing more can be done till I see Mr. Fane. As the woman was in his house, he must know----" "He knows nothing," interrupted Laura imperiously; "he can't know. The man is ill at the seaside and----" Derrick interrupted in his turn. "I'll wait till I hear what Mr. Fane has to say," he declared abruptly. He rose to terminate the interview. As he opened the door Tracey entered hurriedly. "My car's found," he burst out. "Where?" asked Derrick and Laura together. "Stranded in the yard of Charing Cross Station." Laura turned quickly on Derrick. "I beg you to observe, Mr. Inspector, that you cannot get to Westcliff-on-Sea from Charing Cross." "I have not yet accused Mr. Fane," retorted the inspector. CHAPTER V PUBLIC OPINION