"I wonder," said Derrick; "and who could have killed her?" "That is the mystery," sighed Laura, turning to go away. "It will not remain one long. Mr. Fane must know her, since only he had the latch-key." "Yes. Only he has----" here Laura broke off and flashed an inquiring look on the inspector. "Do you mean to say that my brother-in-law knows something about this crime?" "If only he has the latch-key----" "You stated that this young man with a pointed beard met by your policeman had a latch-key." "Yes. But has Mr. Fane a beard?" "A beard? No. He is clean-shaven." "He might have assumed a disguise." "How dare you hint at such a thing?" said Laura indignantly. "I am quite sure that Mr. Fane knows nothing. Last night he was at Westcliff-on-Sea, ill in bed. I can show you a wire. My sister knew that I was going to her to-morrow, and she wired last night at five o'clock saying that Walter was ill and that I had better not come." "Oh!" This statement took the inspector aback. If Fane had been ill at Westcliff-on-Sea, he certainly could not be the man met by Mulligan. "Can you show me the wire?" he asked. "I will send it round to you. And I am quite sure that when you see Mr. Fane you will not suspect him of this crime. A better and more kindly man does not live. However this woman came to enter the house, however she was killed, and for what reason, Mr. Fane can know nothing of the matter. How was she killed?" "Stabbed under the left shoulder-blade while she was singing." "Singing! What was she singing, and why in a strange house?" "She was singing 'Kathleen Mavourneen.'" Laura looked surprised. "My sister's favourite song." "Oh indeed," said Derrick sharply. He hesitated. "Your sister is also at Westcliff-on-Sea?" "Are you about to accuse her?" asked Laura disdainfully. "I accuse no one," replied Derrick, nettled. "I am only trying in all directions to learn facts upon which to build up a theory." "Then why don't you look for real evidence?" "Such as what, Miss Mason?" "Such as the weapon with which this woman was killed." "We have looked. It cannot be found. The murderer took it away. He would not be such a fool as to leave that lying about. The doctor fancies from the nature of the wound that it must be a long slim dagger--a kind of stiletto." "Such as a foreigner might use," said Laura involuntarily. "What do you mean?" asked the inspector sharply. Laura flushed. "Nothing, nothing," she responded; "but foreigners usually make use of such a weapon, don't they? An Englishman would not kill a person with a stiletto." "It's not British, certainly," said Derrick, with insular prejudice; "but a woman might use such a thing. Still, we do not know that the assassin is a man or"--he looked straight at her--"a woman."