"Through my incorrigible laziness," added Duane, with a drawl in her voice. "How I blessed Miss Vacher at that moment for disturbing me!" "Begin at the beginning," advised Miss St. Leger. So the head prefect told her story, quite simply and with some embarrassment, her two listeners hanging intently upon every word. It seemed that Erica, in her blind, childish adoration of the redoubtable Peggy O'Nell, regarded that rebel's natural enemy, the head prefect, in the light of a hateful tyrant. Her highly-coloured imagination, in fact, exaggerated and magnified the attempts of the prefect to put down the junior leader, and after the ordering-off of Peggy from the sports field, her seething indignation crystallized into a fierce determination to avenge the insult offered to that much-wronged damsel. How this was to be accomplished she had no idea; probably her feelings would have calmed down before long without any harm whatever being done, but a few chance words from Bertha--words not said in a very kindly spirit--put the whole idea into her head, an idea which would otherwise have never entered it. The Richoter candidates had been giving an account of their morning's experiences in the laboratory, when they left it for the dinner hour. Bertha, with Erica, had been among the listeners. Strolling off afterwards, the older girl, speaking her thoughts aloud, had said with a laugh: "Now, a very simple way of upsetting any of their apple-carts would be to meddle with the balances just now. A little weight stuck underneath the pan with a piece of putty would do the trick. Simple but effective, eh?" It had been carelessly spoken and Bertha did not dream that anyone had taken notice of her words, or in fact heard them, save her little sister; and Erica, fired by impulse, resolved in that way to avenge the wrongs done to Peggy and her confreres by the tyrannous head prefect, who was so mean and horrid to them. It never occurred to Erica that the laboratory door might be carefully locked to ensure against any tampering with the unfinished experiments. A weight? A little piece of stone would do. Putty? A bit of plasticine out of one of the tins in her classroom, which was quite near the laboratory! The school-rooms would be deserted now; no one would see her. What could be simpler? And if Duane didn't get her experiment correct, it would serve her right. Oh yes, she deserved it all! Had Erica paused to think, it would never have been done. But the blind impulse aroused by her passionate adoration of Peggy, drove her straight into the school and up the stairs towards the laboratory.