picture man, and from the way he talked I guess he don't know much good of him. Anyhow, while Townsend was looking through some documents he had taken from his pocket, the picture man—Jurgens by name—grabbed a paper and made off with it. Great spark plugs! I never saw a more brazen piece of work. I chased Jurgens out on the steel pier, but he got away from me by taking to a rowboat that was moored there."

Ferral laughed. The idea of Carl mistaking what was going on and trying to save a girl from pirates, there in that fashionable resort, was too much for him. Temporarily he lost sight of the graver aspects of the affair. Even Matt grinned at the spectacle the Dutch boy, in his bathing suit, must have made, battling with pirates to save a girl who did not want to be saved.

"This thing has got a mighty serious side to it, Dick," said Matt, suddenly sobering. "I haven't the least notion what that paper was that Jurgens grabbed, but it must have been an important document. And Townsend lost it while trying to help Carl and me. That puts it up to us, Dick, to help him get it back."

"Right-o!" returned Ferral. "There's a boat putting off from the Heinz pier. McMillan's in it and two men are breaking their backs at the oars. They'll get this Jurgens swab, if I'm any prophet. They're going about two fathoms to Jurgens' one."

"How's Jurgens heading?"

"For the open sea. He's struck rough water just over the bar from the Inlet, and his boat's on end about half the time. If one of those combers hits him broadside on, he'll go to the sharks, paper and all."

"What's his notion for heading out into the ocean, I wonder?"

"Strike me lucky!" exclaimed Ferral. "Why, he's making for a sailboat, and the craft is laying to to take him aboard."

"What's the name of the boat? Can you make it out?"

The sun was down and shadows were settling over the water. Enough light remained, though, for the sharp eyes of Ferral to read the name on the sailboat's stern.

"She's the Crescent," he announced, "and one of the boats that berth in the Inlet. There! Listen to that!"

The crack of a revolver echoed up to Matt and Carl above the surge of the breakers.

"Who's doing the shooting, Dick?" asked Matt.

"McMillan. He sent a bullet across the Crescent's bows. That's an order for her to keep lying to until McMillan can come aboard. They're just taking Jurgens out of the boat and making the boat's painter fast. Ah!" There was excitement in Ferral's voice as he went on. "The skipper of the Crescent isn't obeying orders, but is going on out to sea. I'll bet McMillan is as mad as a cannibal. There he goes, blazing away at the Crescent—but he might as well throw his bullets into the air."

"The Crescent will be called to account for that!" exclaimed Matt.

"McMillan is pulling back to the pier," proceeded Dick, watching below. "What are we to do now, matey? We'd have had considerable trouble taking Jurgens off the rowboat, and it's a cinch we can't get him off that other craft."

"We'll follow the Crescent for a while," said the young motorist, "and see where she goes. Possibly she'll try to land Jurgens at some point on the mainland. If she does, we'll drop down there and do what we can to capture him."

For more than an hour the Crescent steered straight out into the ocean, the Hawk hovering above her. The sailboat was not putting out any lights, and the growing darkness rendered it impossible for Matt or Dick to see any one aboard her. They could hear voices, however, for sounds on the earth's surface are always wonderfully distinct to people in balloons or other air craft.

At the end of an hour and a half the Crescent put about. The Hawk followed the sailboat as far as the channel leading through the bar at the entrance to the Inlet. Having made sure that the sailboat would return to her usual berth, the boys headed their air ship for the beach.

"I guess McMillan will be on the lookout for the Crescent, Dick," said Matt, "but we ought to make sure that Jurgens don't get away. I believe I'll get out of the Hawk, close to the Inlet, and leave you to take the air ship back to her moorings."

"I can do that all right, messmate," answered Dick.

There was plenty of room for landing, and when the Hawk had been brought within a couple of feet of the ground Matt dropped over the rail and Ferral took his seat among the levers.

As Matt hurried to the board walk, and on to the wharf at the Inlet, he looked around him for some officer whom he could pick up and take along with him. There was no officer in sight, however.

It was the dinner hour at the big hotels, and promenaders had nearly all deserted the ocean front. A dozen or more sailboats were heaving to the swell and knocking against the wharf at the Inlet, but only a few of the men belonging with them were on the wharf itself.

"Can you tell me where the Crescent is?" Matt asked of a man leaning against an electric-light pole.

"Jest seen 'er standin' in," was the reply. "She ought to be at the end of the wharf by this time."

"Is that where she lies when she's tied up?"

"Yes."

Thinking that surely he would find McMillan, or some other officer, at the end of the wharf, ready to deal with Jurgens the moment he tried to come ashore, Matt hurried on.

The Crescent had just warped into her berth. A man on the wharf was making her cable fast. Under the electric light Matt could see a group of three or four men in the cockpit of the little sailing craft. At about the same moment, a figure lurched forward from behind a barrel that stood on the wharf. The gleam of a star on the coat informed Matt that the man was an officer.

"Hello, there!" the young motorist called to the group in the cockpit. "Where's that man you picked up off the Heinz pier?"

Two of the men climbed to the side of the Crescent and jumped to the wharf planks. Neither of them was Jurgens.

"You've got us guessin', friend," said one of the men.

"Not much I haven't," answered Matt, stoutly. "I was one of those in the air ship and I saw you pick up Jurgens."

"You've got him, all right," put in the officer. "He's a thief, and I'm here to arrest him. The Crescent is liable to get herself into hot water by this afternoon's work."

The officer was not McMillan. While he spoke, he started for the edge of the wharf with the apparent intention of getting into the sailboat and making a search.

"Hold up a minute, officer," called the man from the Crescent, pulling off his coat.

The officer halted, and turned. At that instant, Matt saw the fellow who had been making the boat's cables fast to the posts, creeping toward the officer from behind.

"Look out, there!" he yelled. "One of those men is after you from the rear! They're trying to——"

Matt's words were cut short. While he was speaking, the man from the Crescent had whirled suddenly and thrown the coat over his head.

Matt had a fleeting glimpse of the officer, crumpling to the wharf under a vicious blow from behind, and then his own head was encompassed in the smothering folds of the coat and he was thrown struggling to the planks.

CHAPTER IV.

PRISONERS ON A SUBMARINE.

Motor Matt fought in vain to free himself. At least two men had laid hold of him, and the coat was kept drawn tightly over his face and head to prevent outcry. In this condition he was picked up, carried some distance along the wharf and finally laid down on his face while his hands were lashed at his back and his feet tied. Then, perfectly helpless and unable to see where he was being taken, he felt himself lifted and lowered. After a moment he was lifted and lowered again, this time, as he surmised, through a narrow hatch, for he felt