He began to scramble up the flimsy ladder.

Hardly had he ascended four rungs than there came an alarming crack!

"Look out!"

Frank clung to the rung above, just as a rung snapped beneath his weight. He hung in midair for a moment, then drew up his feet and placed them on the next rung. This proved firmer, and he was able to go on.

"Don't break 'em all," called Joe. "I want to be in on this."

Frank continued up the ladder. Occasionally, when he came to a place where a rung had broken off, he was obliged to haul himself upward by main force, but finally he neared the top. The ladder ran up along the side of the tank to the very top of the great, vat-like receptacle, and there it led to a trapdoor.

The Hardy boys did not look down. They were high above the ground now, and the old water tower was swaying alarmingly. They began to realize their peril, for the tower was old and liable to topple over with them. But the thought did not serve to restrain them, and at last Frank scrambled over the last rung and found himself on the upper surface of the tower. He turned around and helped Joe over.

Far below them lay the countryside, the green fields laid out in neat patterns, the roads in the distance like white ribbons, and the railway tracks glistening in the sunlight. The wind seemed much stronger on top of the tower, and it whistled about their ears. The flimsy structure swayed to and fro with every movement they made.

The trapdoor was closed. Frank went over to it and tugged at it, but the timber was heavy and Joe was obliged to help him. Between the two, however, they managed to raise it, revealing a dark gap that led into the recesses of the abandoned water tower.

The upper part of the tank was a space about four feet in depth and separated from the lower, or main portion by a thick floor. Frank lowered himself through the opening, and he was quickly followed by his brother. They crouched down below the roof of the tank and peered about them in the obscurity.