“Wait a while,” encouraged Gincy, ignoring the insinuation. Personally, she was not fond of Lalla, whose keen wit never spared any one, but of all the mountain pupils she was the most talented—so the teachers had said—and Gincy was working for the good of the school.

“I’ve got hit to work out and I’m goin’ to do hit,” she said to herself that night. “I reckon Lalla’s plumb out of patience or she wouldn’t be so touchy.”

She took a firmer grip on the baffling mental problem, her detective instinct now fully aroused. Things happened at dinner time. Mallie and Nancy Jane were nearly always at meals—and yet—Gincy thought over every other girl in the Hall; not one seemed to have either the disposition or the ability to carry on, undetected, such a warfare.

At six o’clock that evening, she was behind the door of Number 16, the new master key showing temptingly in the lock. She had figured it all out; the room must be watched from the inside. This time both window and door were to be reckoned with. She raised the former to further her scheme, and told no one except Miss Howard, who promised to bring Gincy’s dinner to her own room that she might eat it later.

It was a weary vigil, but Gincy worked out some problems and waited patiently. The hour was almost gone when a slight tap came at the door. She crowded behind a dress in the corner and listened eagerly. The door swung slightly and Nancy Jane Ping looked in. Her small, inquisitive eyes seemed to pierce every corner, and Gincy had a breathless moment of expectancy. Kizzie’s yellow muslin was a feeble barrier for the gimlet glances to penetrate.

For a moment, the intruder stood keenly surveying the room, then withdrew and walked slowly down the hall. Gincy waited, but she did not return. After all, the evidence was very incomplete. Anybody might have looked into a room whose door was slightly ajar. It didn’t matter how much inward conviction one had if she lacked tangible proof. The whole baffling pursuit had to be begun again, and Gincy united her Scotch persistency and Irish wit afresh.

For a week she was absent from the dining-room at the dinner hour, the most sociable time of the day. It had not been necessary to tell Kizzie or Lalla, or, in fact, anybody, as she sat in the Annex dining-room, and they rarely saw each other.

Still nothing happened, and Gincy went on studying her arithmetic and planning her work for rhetoricals. She did not forget to keep the window open, however, and the shining new master key in the door as a bait. “Whoever hit is won’t resk coming in at the window, they’d be suspicioned sure if any one should open the door.”

She reasoned it all out as she sat motionless on the fifth night of her vigil. Almost at that moment the event which she had been anticipating happened. The key clicked in the lock and she was shut in. For one instant she listened to hear in which direction the retreating footsteps were going—there was a telltale squeak which betrayed it—then Gincy bounded across the room and slipped out of the window. She ran noiselessly to where the halls crossed and a door led to a back stair landing. Gincy knew that she could see from there any one who came down the main hall, while the dark corner was a safe hiding-place for herself.

She had barely gained the desired spot, when some one vaulted past and out upon the roof. It was Lalla Ponder who stole cautiously along and deposited a small, shining object in a convenient niche near the cornice. Gincy could hardly believe her eyes, but when Lalla turned her back, she looked into the main hall and saw that it was entirely empty. She knew that Lalla would not attempt to gain her room by the window, but would come back into the hall and either go down the back stairs or come up boldly and unlock her door. Gincy pounded on a nearby door vigorously, knowing that its occupant was probably taking care of the lamps in the lower hall, then she walked noisily to meet Lalla, who had regained the hall when her back was turned.