"Su—su—SOMEBODY'S knocking on the bottom of the boat." Before he could explain, or tell them anything further, a perfectly terrific knock from below made the Crescent Moon shiver from end to end. Samuel and Ato, leaning over the port rail, turned round so suddenly they bumped their heads smartly together. Next with a scrape, screech and splintering of timber, a giant white horn came tearing up through the decks.

"Whale! Whale!" croaked Roger, falling off the main truck and coasting crazily down to the deck. "Wha—what ever'n ever's that?" he quavered, pointing a trembling claw at the rigid white column between the main and mizzenmasts. Samuel did not even try to explain, for at that instant the ship began to rise, to fall, to lash and plunge both up and down and east and west. Hooking his arms through the rail, Tandy blinked, gasped and shudderingly waited for the Crescent Moon to fly asunder.

"Narwhal, Mates!" panted Samuel Salt, throwing himself bodily upon the wheel. "Horn like a—uni—corn—branch of the Odontocetes and—"

"Oh—you—don't say—it—is!" chattered Ato, who was lying on his stomach bouncing up and down like a ball at each frightful lunge of the monstrous fish. "Well, it's spiked us—is that a horn or a ship's mast? Oh woe, oh! What'n salt'll we do now?"

Samuel had not the heart to answer, for he had all he could do to hang on to the wheel as the ship, like a wounded animal, reared and plunged, thrashing the sea to a fury of foam and spray. Nikobo, diving precipitously off her raft, began to squeal in high and low hippopotamy, making brave but ineffective lunges at the lashing giant beneath the ship.

"Su—suppose it su—submerges?" wailed Ato, who had managed at last to seize a rope from the end of which he banged and slammed continuously up and down against the deck. "Oh, my stars! Oh, my spars! Oh, my beams and—" Tandy never heard Ato's last anguished cry, for at that moment a savage shake of the Narwhal's head sent him flying into the sea. Coming up coughing and choking, Tandy instinctively began to swim and for the first time became aware of the creeping vine he still had clutched tightly in one hand. And in that instant and in that whirl of danger, disaster and destruction, the little boy suddenly grew calm and purposeful. This vine—well, why would this powerful vine from Patrippany Island not work as well under water as on land? The chances were that it would. Swimming boldly back to the ship, Tandy took a quick dive, hurling the vine pot and all in the general direction of the Narwhal. No sooner had the vine touched the water than it began to open, creep and grow and, spraying out a hundred strong tentacles, it seized and bound the plunging monster in a secure and inescapable cradle of leafy wood.

Gasping and sputtering, but with his heart pounding with joy to think he had really saved Samuel's beautiful ship, Tandy rose to the surface. Nikobo, letting off shrill blasts of anger and fright, came paddling anxiously toward him. But giving the hippopotamus a reassuring wave, Tandy seized the end of a rope ladder and pulled himself up to the deck.

Samuel, though battered and bruised, still clung to the wheel, and Ato, almost pounded to a jelly, had rolled into the scuppers where Roger was fanning him vigorously with a butter paddle. The Read Bird, having wings, could have left the ship at any time, but had clung bravely to his post, preferring to go down with the ship and his shipmates. Now all three of them stared in dazed silence at Tandy as he climbed back over the rail, for in the terrible confusion and excitement no one had seen him go overboard.

"Tandy! Tandy! Where've you been?" With outstretched arms Samuel Salt rushed groggily forward. "Shiver my liver! Why's everything so quiet? Could it be that you single-handed have destroyed that ship-shaking menace?"

"I don't think he's destroyed, Master Salt," answered Tandy, limping happily to meet the Captain, "but he's caught fast as a lobster in a lobster pot and can't move at all."

"Caught?" rasped Samuel, running across the deck to peer over the rail.

"By the creeping vine," explained Tandy, and in short, breathless sentences he told them all that had happened after he was flung into the sea.

"Well, bagpipe my mizzenmain sails!" gasped Samuel Salt, staring at Tandy with round eyes. "This is the strangest and happiest day of my life. You've saved the ship and the whole expedition, my boy, and all we have to do now is cut loose from this cavorting unicorn of the sea and sail off with the largest ivory horn in captivity. An ivory mast, blast my buckles! Wait till the Ozites see us sailing up the Winkie River with four masts instead of three! Ahoy, below! Ahoy, Kobo! Can you dive with me beneath this ship?"

"Dive and stay under as long as you can," vowed the hippopotamus, shaking the water out of her eyes and looking cheerily up at the Captain. "You see, I was right about those creeping vines, now wasn't I?" Nikobo, having done a little investigating on her own account, was well nigh ready to burst with pride at Tandy's quick action and the way in which the vines had overcome their gigantic foe.

"RIGHT!" boomed Samuel Salt, hurrying off for his oxygen helmet and powerful diamond toothed saw. Ato was too bruised and exhausted to rise, but Tandy and Roger, perching on the ship's rail, watched Samuel in his queer diver's helmet climb down the rope ladder and clamber up on the hippopotamus. Next minute Nikobo had disappeared under the surface and presently from the slight shiver and shake of the boat they knew that Samuel was determinedly at work cutting them loose. Fortunately there was room between the ship's bottom and the whale's head for Nikobo to swim about, and so splintering sharp was Samuel's saw that in less than five minutes he had cut off the great column of ivory level with the ship's bottom, carefully calking the edges with material he had brought down. In its tight and live wood crate the Narwhal could not stir an inch, and, while the cutting of its horn was not painful, it blubbered and spouted so terrifically that Samuel and Nikobo heaved tremendous sighs of relief when the dangerous operation was accomplished.