Like a picture ship on a blue enameled sea, the gunboat Gatoon steamed quietly on her way. Not even a ground swell disturbed the level of her white decks, or raised an extra dash of spray from her cutwater.

Yet storm and violence, in human form, were already aboard her. Within the vessel’s narrow confines, loyal officers and citizens of a great nation were pitted against the unknown agents of a fiendish power. Each side now stood on its guard, ready for the battle to open; but when or where the first blow would be struck, only the Scorpion himself could tell.

The strain of waiting was hardest, of course, upon Don and his friends, who at this moment were gathered under an awning on the Gatoon’s after deck. They knew that one or more of Scorpia’s agents were on board, disguised no doubt as members of the gunboat’s enlisted crew.

They were aware that the enemy would stop at nothing—not even at destroying the ship with every living soul—if that could be accomplished. Yet they were helpless to do a thing until trouble showed itself in visible form.

Don Winslow, standing by the after rail, had just finished telling about the spy he had almost caught listening at his cabin door. That incident fitted perfectly with the theft of Michael Splendor’s decoded letter. Unfortunately, the brief glimpse Don had had of the skulker was not enough to identify him.

“All I saw,” he admitted, in response to Captain Riggs’ query, “was a man’s white clad arm and shoulder disappearing around the corner of the bulkhead. It didn’t look like a seaman’s blouse!”

“You mean, it might have been an officer’s, Don?” cried Mercedes Colby, leaning forward in her deck chair.

“Or a petty officer’s or even a cabin steward’s,” responded the young commander. “That really isn’t much to go on in naming a suspect, you see.”

“I’m sure, Winslow,” said Captain Riggs stiffly, “that every commissioned officer here aboard is above suspicion. As for the enlisted personnel, of course, I can’t be sure. There were some replacements made in the crew before we shoved off from Guantanamo, and a spy might have come aboard with them. About the only thing we can do is to check their enlistment records.”

“The very idea I was about to suggest!” agreed Michael Splendor. “Suppose you and Commander Winslow look through the papers now, Captain, and let us know what you find. Meantime, Lieutenant Pennington and I will try to entertain Miss Colby. We’ll meet again at mess, this evening, if nothing happens before then.”

When Don and the captain had gone below, the man in the wheel chair turned his keen blue eyes on the two young people beside him.

“Sometimes, me friends,” he said earnestly, “I have a hunch that some great thing is going to happen. And happen it does, despite every circumstance against it. In this case me hunch is that the Scorpion’s power will be broken, and himself a prisoner, six months from this very day!”

A low whistle from Red Pennington greeted Splendor’s statement.

“But those were almost my own words to Don this morning!” the stocky lieutenant exclaimed. “Thanks to Don Winslow, we’ve matched every move the enemy has made with a better one. The Scorpion must be desperate, right now. And desperation usually goes before a flop, doesn’t it?”

“Very often, it does,” replied Michael Splendor cautiously. “But I’m afraid the Scorpion is more angry than desperate at this moment, for all the damage we have done him. 'Tis rather because of that code letter, and the opening it gives us, that I’m so hopeful of success. As you recall, it tells us there is to be a meeting of Scorpia members in San Francisco, with Cho-San himself in charge!”

“And who,” asked Mercedes Colby, as Splendor paused, “is this person you call Cho-San?”

Once more a look of gloomy absorption had spread across the crippled man’s features. His eyes, gazing outboard upon the sunlit Caribbean, had the look of a sleepwalker’s.

“Cho-San,” he murmured, “is a chosen member of the inner circle of Scorpia. It was he and his evil master, the Scorpion, who made me the cripple I am today. 'Twas their devilish torture, in the chamber of horrors they call the Dragon Room....”

A shudder gripped the big, helpless body of Michael Splendor, cutting off his strange speech. When it had passed, he sighed and blinked rapidly, like a man awaking from a nightmare.

“What was I speaking about? Ah, yes, I remember!” he said in a stronger voice. “Cho-San is the Scorpion agent in charge of all war-provoking operations from San Francisco to Singapore. Any meeting which he calls among Scorpia’s members is of the utmost importance. It means a fresh attempt to stir up war among civilized nations, so that, from the wreckage of human lives and fortunes, the Scorpion may pick more bloodstained wealth and power. The Naval Intelligence knows all that, but we need legal evidence before we can trap the archcriminal.”

“I see what you mean now, sir!” put in Red excitedly. “You’re hoping that Don Winslow may be able to horn in on that secret meeting in some way. If he could do that, he’d get the evidence you need!”

At Splendor’s nod of assent, Mercedes Colby caught her breath sharply.

“But wouldn’t such an attempt be horribly dangerous?” she protested. “Just supposing they caught Don eavesdropping, or present in disguise—what chance would he have of getting out alive?”

“Very little, I am afraid,” replied the man in the wheel chair. “But remember, my dear, the United States Navy is a fighting service, where men and officers expect to risk their lives in the cause of peace. Look! Here comes Captain Riggs, and he seems to be in a hurry. Perhaps he has news....”

The captain took the short ladder to the yacht’s poop deck in two leaps. His expression showed both worry and anger.

“Lieutenant Pennington!” he clipped out harshly. “I’m afraid you’re needed below, in my cabin. Commander Winslow....”

He paused, biting his lip as if at a loss for further speech.

“Go on, sir!” prompted Red in a strained voice. “What’s happened to Don? Has he been taken sick?”

“He’s been attacked!” blurted Riggs. “Struck down from behind and then chloroformed. The doctor is with him now.”

Red waited for no more. Forgotten were gassed lungs and wobbly knees as he plunged down the ladder and dived into the cabin country, several jumps ahead of Riggs himself.

Moments later Splendor and Mercedes Colby joined the anxious little group. Don Winslow was sitting up in the Captain’s swivel chair, looking decidedly “green around the gills.” The ship’s doctor was binding a compress about his head; and, despite the draft through open door and skylight, the whole cabin smelled of chloroform.

“I guess you people will have to tell me what happened,” the young commander was mumbling. “One minute I was looking through a pile of enlistment records—and the next, I was lying on the deck under the table, and feeling sick as a pup! What fell on me, anyhow, Doc?”

“A piece of lead pipe, to judge by the swelling,” growled the medical officer. “Someone wanted to put you to sleep in a hurry, and keep you that way. He used chloroform after slugging you.”

“You sure came out of it in a hurry, though, Don!” laughed Red Pennington, rather shakily. “I’d no sooner picked you up off the deck than you up and socked me in the eye!”

“I’m still slug-nutty; so you’d better watch out, Mercedes!” grinned Don, taking the glass of water the girl handed him. “But, seriously, I’d like to know who downed me, and why. Have you any idea, Captain Riggs?”

“Yes, Commander,” answered the officer gloomily. “I believe it was a brutal attempt at murder by some one of the enlisted personnel. I shall do my best to hunt the scoundrel down before we reach port. Meantime, I can only blame myself for leaving you alone. If I had not returned when I did....”

“Don’t take it that way, Captain!” protested Don Winslow, earnestly. “You weren’t to blame. And as for the notion of a murder attempt—wouldn’t a killer have used something surer than a blackjack and chloroform? Those things are a thief’s weapons.”

“Exactly, Commander!” spoke the deep voice of Michael Splendor. “Ye’ve named the means and the motive all in the same breath. A theft it was, to be sure; and if ye’ll just glance about the place, ye’ll see quick enough what the rascal stole.”

A startled silence fell upon the other five persons in the cabin. It was broken when Don, struggling up from his chair, cried sharply:

“The enlistment records! They’re gone, the whole stack of them!”