Scotty hooted, and pointed. Directly ahead was a small shelf. Rick moved to Scotty's side and saw the dark opening of a cave. Next to the opening was a small octopus. As they approached he changed color, trying to imitate the multicolored coral against which he rested.

Rick reached out a hand and the animal retreated, sliding into the mouth of the cave. Apparently this was his home, because the ledge was littered with sh.e.l.ls from a number of meals.

Now Rick wished for his camera, then smiled inwardly. To satisfy all his unexpected wishes he would need a sort of underwater trailer to tow his gear.

Scotty moved close to the octopus and it retreated still further. Both boys knew the creatures were harmless to divers, and some divers even handled them. But there were reports of divers being bitten while playing with octopuses, and they had learned long ago that unnecessary risks were foolish.

Rick suddenly rocked back as his ears were smitten by sound. A wail echoed in his head, so intense that it almost hurt. Scotty started, too, and reached for the ledge in his astonishment.

The octopus peered out of the cave, and the wail came again, buzzing uncomfortably in their heads. And in that moment, Rick's air gave out.

He pulled the reserve lever and planed to the surface, Scotty close on his heels.

On the _Water Witch_ they stared at each other.

"Did you hear that?" Scotty demanded.

"I'll say I did!"

"That octopus wailed," Scotty insisted. "Twice!" He hesitated, then put Rick's thoughts into words. "Only--octopuses don't wail. They don't make noise of any kind."

"This one did," Rick said. "A wailing octopus! This is either a new scientific find, or ..."

"Or we've found what the fancy frogmen didn't want us to find," Scotty concluded.

CHAPTER XI

Lights on Clipper Reef

"This," Hobart Zircon boomed, "is a phenomenon that will rock the science of zoology to its very depths! We will examine this creature and determine his genus and species, and we will name him after you two.

_Octopus waili branti-scotti._ Or perhaps _Octopus screami_ would be better."

"Of course we're not certain that it was a wail," Rick said soberly. "He might have been singing. He might even have been telling us to go catch him a fish."

Tony Briotti observed, "This may not be an isolated phenomenon. Who knows? A search may disclose screaming squid, or simpering sharks, or burbling barracuda."

"Seriously," Zircon asked, "have either of you a theory to account for this? Or do you really believe that the octopus wailed?"

"We'd be in a better position to answer that if we'd had a chance to explore the cave," Scotty replied. "How can we tell? Maybe the octopus really did wail, and we were the lucky ones who heard the sound for the first time." He grinned. "We should have wailed back and tried to strike up a conversation."

Rick agreed. "I'm with Scotty. We just don't know. I agree that a wailing octopus is a new kind of beast, but that's not entirely impossible, is it?"

"Perhaps not." Tony stared at the sunset. "I'm trying to recall the physiology of _Octopus vulgaris_, as the garden variety of octopus is called, but my memory isn't working. It isn't beyond reason. After all, some fish make sounds. I've caught croakers myself that were pretty noisy. But I've never heard of octopus sounds until now."

Scotty chuckled. "Haven't I read that octopuses have some intelligence?

We might teach him to sing. He'd be a natural for television."

"You say that the sound was loud?" Tony asked.

"Very loud. My head hurt. Did yours, Scotty?"

"I'll say! For a minute I thought my brain cells were rubbing together."

Zircon sighed. "I am stumped. And not only by your Wailing Willie, either. This whole affair baffles me, including the presence of Steve's former tail on this island. Hasn't it occurred to you that those fancy frogmen, as you call them, would have made some overt move by now if they were really interested in us?"

"Dropping the chicken was an overt move," Rick pointed out.

"Yes and no. I'd prefer to call it a not-too-subtle warning. Yet they haven't tried to interfere with your diving around the wreck."

"I've wondered about that," Scotty offered, "and it seems to me they've satisfied themselves that our interest is just in the wreck, and not in whatever they have hidden underwater. If they have anything hidden, I mean. As long as we stick with the wreck, they have no reason for causing trouble."

Tony agreed. "That makes sense to me. Perhaps you can answer this: Why do they wear cold-water suits? It's appreciably cooler at twenty fathoms, but it's certainly not cold enough for a suit."

"We only stay down fifteen minutes," Scotty said. "If we stayed down longer we might get chilled. The water isn't warm by any means down by the wreck."

Rick had a thought. "We're used to cold water, remember? Diving off Spindrift would chill a polar bear, even in summer. Suppose these people had done all their diving in tropic waters? This water would seem cold to them, particularly down deep."

It was nearly dark now, only a glimmer of light in the west. The four sat on the front porch of the cottage.

Zircon asked, "Did you monitor the radio tonight, Rick?"

"Yes, but there was no word from Steve."

"Don't you think he might like to know about the presence of his shadow on Clipper Cay?" Tony inquired.

Rick pointed to the Sky Wagon resting on the beach. "Trouble is, that's our only communication. I could contact the St. Thomas airport and request that they pa.s.s a message, but that would be like broadcasting it to the world. Steve might not like it."

Zircon's deep voice cut into his comment. "Look! Our friends are apparently going to do some night work."

There were lights on the frogmen's boat, and it was putting out. As the Spindrifters watched, it slowly approached the reef, then stopped.

Scotty got the gla.s.ses and examined the scene. "Something's up!" he exclaimed. "I saw a diver go over the side!"

Hobart Zircon coughed self-consciously. "Do you know, I have taken a certain amount of pride in the fact that I am by nature a conservative individual with a highly developed capacity for minding my own business."

Rick wondered what on earth the big scientist was getting at.

"The pursuit of truth has led me along many devious routes," Zircon continued. "I have tried, with some success and many failures, to plumb the mysteries of Nature. But while I have tried to make the business of our natural universe my own, I have never thrust my not-inconsiderable nose into the business of neighbors. However, this admirable reticence has limits, since, as a scientist, I am also possessed of that inherent trait of curiosity without which no person can succeed in science."

Rick exploded into laughter. "And what you're leading up to is, you want to go see what those people are doing!"

"Precisely," Zircon admitted.

Tony and the boys roared with laughter.

"Hobart," Tony said with a chuckle, "you never fail to astonish me. And how do you propose to stick your not-inconsiderable nose into the business now going on over there?"