"Quite sure, Miss St. Leger. I always lift them before using, to test and correct them, if necessary. I distinctly remember testing them this morning." "Then that means that someone has tampered with them between then and when we returned," interposed Miss Vacher. "Exactly. But surely it was not possible for anyone to touch them while you were working in the room. Constance, what do you say? You should be the best judge of that." Salome raised her eyes frankly to the Principal. "I have been thinking of that, Miss St. Leger. It seems quite impossible to me. I did not leave my place after the weighing till we went out about ten minutes later." "And the nearest girls to you?" "Eileen and Duane, and they were right at the farther ends of the benches. I am quite sure no girl in this room touched them then." "Who was the last one to leave the room?" "Eileen and I. We came out together with Miss Vacher." "You are quite sure of that? No one was left behind, even for a half minute or so? It could have been done in a few seconds." "I was the last out, Miss St. Leger," replied the science mistress, "and I locked the door after me." "Most extraordinary," said the Principal, "and there is only one key to that lock in the school. We found _that_ out last year. The key never left your possession during the dinner hour, I suppose, Miss Vacher?" The science mistress was looking far from happy. "The key was not in my possession, Miss St. Leger. After last year--I mean, owing to my unfortunate absent-mindedness--I decided to entrust it to somebody else. Duane took charge of it for me." "Oh!" Miss St. Leger's expression changed abruptly. No longer did she look puzzled, but keen and alert. "I am rather sorry for that. However, Duane will be able to answer that question for us." Duane hesitated, looking across at the science mistress. "Only once, Miss St. Leger. Miss Vacher sent a junior asking me to get a pipette out of the lab for her, as she wanted it for some private work she was doing in her room. I was--was feeling rather lazy, so another girl offered to fetch it for me." "Who was the girl who fetched the pipette?" "Kitty Despard." Miss St. Leger nodded. "Ah yes, I remember. The girl from Australia, who came at the beginning of the term. When was this?" "Just before dinner." "How long was she gone?" "Only a few minutes." "She gave the key back to you on her return?" "Yes." "What did you do with it then?" "I put it back into my pocket." "And it stayed there till you handed it to Miss Vacher?" "Yes, Miss St. Leger." "No one could have taken it and put it back again unknown to you, I suppose?" Duane shook her head decidedly. Miss St. Leger turned to Eileen. "Will you please see if you can find Kitty Despard for me, Eileen, and ask her to come here. She is probably down on the playing-fields, as afternoon lessons are over. Don't say anything to Kitty or anyone else about what is happening here."