many other things.

Of a sudden, their conversation was interrupted by a sound, conveyed through their head-phones.

“Sh—“—Doris’ hand went up. “It’s that strange whisper again!”

“Whispering waters!” Mildred murmured. “How mysterious!”

Low as her tone was, the whisperer apparently caught it, for—still in that hoarse whisper—there came back:

“So we are mysterious! How very grand! And it was a lady who spoke!”

Once again Dave’s voice broke in upon the whisperer: “Doris!” Tenseness was evident in his tone. “Doris!—Tell them to hold us right where we are!”

“Hold it!” Doris called to the windlass man, instantly.

“Hold it,” came back the quick acknowledgment.

“All this,” Doris said to Mildred, “is most provoking. You are just dying to know what strange things are happening below, what marvelous discoveries are being made—but the only part you have in it is listening and waiting!”

Down in the steel ball, Dave had caught a movement to the right, away from the cliff. Switching his light in that direction he had discovered a huge, dark object moving slowly through the water.

“It’s that ‘thing’!” he told himself. “The very thing I’ve seen before!”

To his great disappointment, the form was as indistinct as before. That it might be a whale he knew quite well. He suggested the idea to Johnny.

“But it’s not a whale—I’m sure of it!” Johnny whispered. Swinging his moving-picture camera into range, he managed to catch the rear half of it before it passed from view.

“The camera sees more than the eye,” he murmured. “Here’s hoping.”

Dave turned again to his task of exploring the under-sea wall. He signalled their continued descent.

A moment later the ear-phones on deck were silent. Both Dave and the mysterious whisperer were unheard.

“Who could that have been?” Mildred asked.

“I’ve no idea,” was Doris’ reply.

“Do you know,” Mildred added dreamily, “I have a feeling that whisperer was not far away!”

Doris started to speak but checked herself, suddenly. Once again she had caught the weird tones of the whisperer.

“One-eighty—eighty-two—eighty-six,” he droned. Then he raised his voice above the whisper, and called:

“Hello there—you mermaids! Are you still there?”

“He must be near us!” Doris exclaimed. “If not—why would he call us ‘mermaids’?”

* * * * * * * *

At that same instant Dave was experiencing a thrill. Arrived at a spot opposite a broad shelf on the perpendicular wall, he and Johnny found themselves within five feet of the rock. Vegetation, which had been thinning out, was just disappearing.

And then Dave saw it—a long, wavering arm, reaching out for the steel ball. Involuntarily, he started back from the window. Then he laughed.

A second arm appeared. Then, a third.

“Octopus!” he whispered to Johnny. “Such a monster!” Instantly his light was on, and Johnny’s movie camera was grinding away.

“Only one of his kind I’ve ever seen!” Dave was thrilled to the tips of his toes. “Wish he’d climb on board and let us take him up. He won’t do that, but I’ll get him, all the same! Some time I’ll get him!

“How ugly he is! See how his eyes shine, Johnny! People sure would throng around him in an aquarium! Put him in with some gorgeous, tropical fish and you’d have a ‘beauty and the beast’ show! You—”

Suddenly he stopped speaking, to stare straight at the wall. They were moving away! There could be no doubt of it. Fascinated by the strangeness of the situation, he and Johnny sat motionless while the octopus faded from sight. Two yards—three—five—ten—twenty—they were swinging off! And behind him was a second wall, against which the window of the steel ball might crack like an egg shell.