They continued to crouch there and watch what went on, their eyes glued upon the dimly seen figure of the unknown. Greatly to the surprise of Thad, the party stepped to one side, and seemed to be dragging back a heavy plank, not of any vast length, but sufficiently long to reach the window when placed on a slant.
"Say, did you notice how he seemed to know just where that plank was lying, Hugh?" asked Thad deliriously. "Seems like he must have been spying out the land by daylight beforehand."
"You're right there," whispered Hugh; "and he acts as if he felt pretty certain that particular window would be unfastened, in the bargain."
"Hugh, that settles it," added the other sturdily, as though now fully convinced.
"Yes, settles what, Thad?"
"Why, it's a boy, don't you see, and he must have left that window unlatched on purpose this afternoon when some of the fellows were shutting up."
"Wait and see," advised Hugh, although almost convinced of the same thing himself.
The test was not long in coming. They could see the other "shinning" up the sloping plank, as any athletic boy would be apt to do, without any particular trouble. Now he had reached the window, and Thad held his breath in suspense. He sighed as he heard a slight squeaking sound. Evidently the sash which was supposed to be fastened every night through ordinary prudence, had given way to his hand, when he exerted some pressure.
"He's going in, Hugh!" Thad observed, again laying a quivering hand on the arm of his comrade, and then following these words with a low exclamation of startled wonder: "Oh! look there, what's that queer glow mean?"
Hugh understood readily enough.