"That's good; but say, Bill, you're off watch to-morrow and I want you to do something for me."

"Anything you say."

"This may involve danger."

"Great Scott, you talk like Sherlock Holmes or a dime novel. What's up?"

"I've got the man who stole those diamonds."

"What!"

"Don't talk so loud. I mean what I say. Listen."

And Jack related everything that had occurred.

"Now, what I want you to do is to watch Prof. Dusenberry, as he calls himself, to-morrow when we get into the harbor. His is an inside stateroom so that he can't throw it out of a porthole from there. He'll most likely go to one at the end of a pa.s.sage."

"Yes, and then what?"

"I'd do it myself but the old fox suspects me, I half fancy, and if he saw me in the vicinity he'd change his plans. You'd better take two of your huskiest firemen with you, Billy. He's an ugly customer, I fancy, and might put up a bad fight."

"U-m-m-m, some job," mused Billy. "Why don't you put the whole thing up to the captain?"

"It would do no good the way things are now, and he might get wind of it and hide the jewels so that they couldn't be found. Anyhow, we've no proof against him till he is actually caught throwing the jewels out in that life-preserver to his confederates in the motor-boat."

"I see, you want to catch him red-handed, but what about those cipher radios?"

"There's no way of proving that I read the cipher right," said Jack.

"Our only way is to do as I suggested."

"I hear that Rosenstein has offered a big reward for the recovery of the diamonds," said Billy. "He's up and about again, you know."

"Well, Billy, I think he'll have his diamonds back by to-morrow noon if we follow out my plan."

And so it was arranged. The next morning Jack received a message from Southampton:

"All ready. Does our man suspect anything?"

This was Jack's answer:

"Not so far as I know. Have a plan to catch him red-handed. You watch the motor-boat."

Saluted by the whistles of a hundred water craft, the _Columbia_ made stately progress into Southampton harbor. As her leviathan bulk moved majestically along under reduced speed, her whistles blowing and her flag dipping in acknowledgment of the greeting, Jack with a beating heart, stood on the upper deck watching earnestly for developments.

He knew that Billy and the two firemen he had selected to help him, on what might prove a dangerous job, were below watching Prof. Dusenberry.

They all wore stewards' uniforms so that the man who Jack believed struck down the diamond merchant and stole the stones might not get suspicious at seeing them about in the corridors.

"I believe they must have changed their plans, after all," Jack was thinking when, from the sh.o.r.e, there shot out, at tremendous speed, a sharp-bowed, swift motor-boat. It headed straight for the _Columbia_. As it drew closer, Jack saw it held two men. Both were blowing a whistle, waving flags and pointing at the big ship as if they, like many other small water craft, were just out to get a glimpse of the triumph of American shipbuilders.

They maneuvered close alongside, while Jack's fingers grasped the rail till the paint flaked off under the pressure he exerted in his excitement. What was happening below? he wondered. Could Billy and his companions carry out their part of the program? Not far from the boy the diamond merchant, unconscious of the drama being enacted on his account, stood, with bandaged head, explaining for the hundredth time the beauty and the value of the gems he had lost.

"Five thousand thalers I give if I get them back," he declared.

Suddenly Jack's heart gave a bound. From a port far down on the side of the ship, and almost directly under him, a white object was hurled. It struck the water with a splash and spread out, floating buoyantly.

Instantly the black motor-boat darted forward, one of the men on board holding a boat hook extended to grasp the floating life-preserver, hidden in which was a king's fortune in gems.

Jack stood still just one instant. Then, driven by an impulse he could not explain, he threw off his coat, kicked off the loose slippers he wore when at work, and the next moment he had mounted the rail and made a clean, swift dive for the life-preserver.

Billy rushed on deck, excitement written on his face, just as Jack dived overboard.

"Jack! Jack!" he shouted.

But he was too late.

"Great Neptune, has the boy gone mad?" exclaimed Captain Turner, who had pa.s.sed along the deck just in time to see Jack's dive. Regardless of sea etiquette, Billy grasped the skipper's arm and rushed into a narrative of the plan he and Jack had hoped to carry out.

"But Dusenberry was too quick for us, sir," he concluded.

"Never mind that, now," cried the captain, "that boy may be in danger."

He looked over the rail, which, owing to most of the pa.s.sengers being busy below with their preparations for landing, was almost deserted.

Billy was at his side. In the black motor-boat two men stood with their hands up. Alongside was a speedy-looking launch full of strapping big men with firm jaws and the unmistakable stamp of detectives the world over. Some of them were hauling on board the police launch Jack's dripping figure, which clung fast to the life-preserver. Others kept the men in the black launch covered with their pistols.

Half an hour later, when the pa.s.sengers--all that is but Mr.

Rosenstein--had gone ash.o.r.e (the diamond merchant had been asked by the captain to remain), a little group was a.s.sembled in Captain Turner's cabin. In the center of it stood Professor Dusenberry, alias Foxy Fred, looking ever more meek and mild than usual. He had been seized and bound by the two disguised firemen as he threw the life-preserver, but not in time to prevent his getting it out of the port. Beside him, also manacled, were the two men who had been in the motor-boat and who, according to the Southampton police, formed a trio of the most daring diamond thieves who ever operated.

"I think we may send for Mr. Rosenstein now," said Captain Turner with a smile. "Only I hope that he is not subject to attacks of heart failure.

Ready," he said, turning to Jack, who stood side by side with Billy, "take these and give them to Mr. Rosenstein with your compliments."

Jack blushed and hesitated.

"I'd,--I'd rather--sir--if you--don't mind----" he stammered.

"You may regard what I just said as an order if you like," said Captain Turner, trying to look grim, while everybody else, but Jack and the prisoners, smiled.

"You wanted to see me on important business, captain?" asked Mr.

Rosenstein, as he entered. "You will keep me as short a time as possible, please. I must get to Scotland Yard, my diamonds----"

"Are right here in this boy's hand," said the captain, pushing Jack forward.

"What! This is the fellow who took them?" thundered the diamond merchant.

"No; this is the lad you have to thank for recovering them for you from those three men yonder," said the captain.

"Professor Dusenberry!" exclaimed the diamond expert, throwing up his hand.

"Or Foxy Fred," grinned one of the English detectives.