As if in answer to his question, Ding-dong Bell appeared in the doorway between the pilot-house and the main cabin.
“Where’s Nat?” he demanded.
“Isn’t he out there with you?” asked Joe, with a quick leap of his heart.
“No. The only person out there is Matco. He’s so scared that he’s under the ber-ber-bunk.”
“Where is the lad?” demanded the professor earnestly, with a note of anxiety in his voice.
Mr. Tubbs, who had been struggling with his dim memory of events preceding his collapse, spoke:
“I recall it now,” he said. “Nat said he was going to get that valve open”—he paused—“somehow.”
“And you let him go?” demanded the professor.
“I—I didn’t mean to,” stammered the repentant Mr. Tubbs, “but I was so nearly on the verge of caving in, that I couldn’t carry out my resolve.”
“Search the craft thoroughly,” ordered the professor, lines of anxiety showing in his face, “there was only one way to open that valve.”