Presently the girls noticed another shack which had been erected in a clump of trees a few yards back from the beach. It was much smaller than the other little house, a mere box-like structure with a flat, low roof.
Walking directly toward it, the man unfastened a padlock and went inside. He closed the door behind him.
“Now what is he doing in there?” Penny fretted, as minutes elapsed and the man remained inside the building. “Listen!”
Both girls could hear a peculiar grinding sound as if from machinery turning inside the shack. The building was windowless, so it was impossible to see what was going on.
“This is maddening!” Penny muttered with increasing impatience. “I wonder—?” She broke off, and gazed thoughtfully at the flat roof of the shack.
“Lou, how is that building lighted?” she demanded.
“From here it looks as if there might be double panels of glass in the roof—a make-shift skylight.”
“Lou, if we could get up there, we might be able to see what is going on!”
“And get caught too!”
“Not if we’re careful. We can climb that tree which brushes against it, and perhaps see from there.”