"It's a queer puzzle," said Frank, as he and his chums looked about.
"It sure is," agreed Bob. "I wonder——"
"Hark!" cried Sammy.
Again came that queer, groaning sound, and it was so close at hand that the boys jumped.
"The noise came from there," said Bob, pointing to the captain's stateroom.
"Maybe—maybe he's tied up in there—hurt," suggested Sammy.
"Maybe—and maybe not!" exclaimed Frank with vigor. "I'm going to have a look!"
His chums glanced at him admiringly. After just a moment of hesitation, Frank tried the knob of the stateroom door. The portal swung open easily, and the boys eagerly looked inside. They were rather disappointed, it must be confessed, when they did not see the body of the captain stretched out in his berth, bound with ropes. The stateroom was empty.
"Well, what—what made that groaning noise?" asked Sammy.