Their air bubbles had been floating to the top of the cabin, forming a pool under the ceiling. But they had stayed in the cabin so long that enough water had been displaced to bring the pool of exhausted air close to the entrance, which was only a few inches below roof level.
In a moment the air would spill out, and rising bubbles would warn the frogmen!
He gripped Scotty's shoulder and pointed to the silvery mass of exhausted air that curled perilously close to the entrance.
The other boy saw the danger at once. He wrote on his slate, "We go whn air duz," and held it in the light for Rick to see.
Rick nodded. He drew his belt knife.
There couldn't be many breaths left before the air spilled out. Nor could there be many before warning constriction forced them to turn on the reserves. At this depth the reserve wasn't very great.
He saw Scotty reach for his reserve lever and pull it down. A moment later he had to pull his own.
Something rang like a struck tank, almost directly overhead!
The lip of the bubble pool moved from the water motion caused by pulling their reserves. Rick watched it, scarcely breathing.
The air pool trembled. A tiny bubble broke loose and sped upward.