A hand found the end of the line and the smooth cylinder to which it was attached. Orvil pa.s.sed very close, and Rick looked upward. He could see the white circle of water around the single propeller.

Now to find out what he had. His hands stroked it from one end to the other. One end was rounded. The other was a circle with an odd-shaped hole running into it. Rick poked his finger in, but couldn't feel the end of the depression. The only protuberance on the thing was a band near the rounded end. The band felt like metal, and had two rings projecting from it. The rest of the cylinder didn't feel like metal. The texture was that of a smooth plastic.

Rick lifted the object gingerly. It was hard to estimate weight under water, but he thought ten pounds would be about right. The total length was less than three feet. It would be easy to carry.

This time he needed a reciprocal compa.s.s course. It would be 260 degrees going out. He oriented himself properly, picked up the cylinder, and began the long swim back. He wondered if Merlin's guards were watching his bubbles. He had seen no sign of bullets, but he hadn't been looking for them. With Orvil's motor so near, it was likely he would not have heard the slap of a bullet on the water.

Pressure told him he was out of the cove. He breathed a little easier.

Now to count leg strokes again. He looked up, and saw that the surface of the water was shining with light, the first rays of true daylight.

Scotty would have no trouble finding him.

Because of the daylight, he continued on for a distance beyond where Scotty had dropped him. No use giving the guards too good a shot.

Finally, exhausted, he surfaced. He lifted his mask and surveyed the scene.

Orvil Harris was still crabbing. Rick could see the boat, but the angle was wrong for him to see the crabber at work. He turned slowly in the water, and saw Scotty. The runabout was floating, motor off, about a mile away. He lifted an arm. The glint of first sunrise turned the lenses of Scotty's binoculars into a crimson eye, and Scotty waved back.

In a few seconds Rick heard the motor start and saw the boat racing toward him. He kept his mouthpiece in place, and floated, waiting.

[Ill.u.s.tration: _Now to find out what he had_]

Scotty came alongside and reached down. Rick handed him the cylinder.

Scotty put it on the seat without even looking at it. He gave Rick a hand and pulled him over the side. He asked anxiously, "Are you all right?"

"Done in," Rick said wearily. "But otherwise okay."

"Let's get out of here." Scotty put the runabout in gear and headed back toward Martins Creek.

Rick sat down and picked up the cylinder. There was a gob of mud still on it. He wiped it off with his hand and examined the thing. The material was fiber gla.s.s set in resin, and it was designed so the rounded nose could be removed. He didn't remove it, however. Instead he looked at the other end, down into the hole with the puzzling shape. It was like a cutout Star of David in shape, the hole gradually narrowing until its apex was almost at the other end.

The light dawned. Rick's lips formed the word. "Grain."

Scotty was watching. "What?"

"Grain," Rick said again. "This thing is a small solid-propellant rocket!"

CHAPTER XV

The Empty Boat

The Swiss torsion clock on Steve Ames's fireplace mantle read 6:49. Rick and Scotty, in slacks, shirts, and moccasins, sat in armchairs and tried to stay awake. The small rocket, cleaned and dried, rested on a newspaper on Steve's table.

"Rockoon," Rick said. "That explains the funny antenna, the presence of the electronics expert, and why the stingarees are launched."

"Not to me, it doesn't," Scotty retorted. He sipped steaming coffee.

"What was that word you used? Grain?"

Rick nodded sleepily. "That's what solid rocket fuel is called. It's poured into the casing around a form. The form is withdrawn after the fuel hardens. The shape is designed to give maximum burning surface.

Since the solid fuel is grainy, it's called grain."

"Logical," Scotty replied with a languid wave of his hand. "All perfectly logical. I also understand that a rockoon is a combination of a rocket and a balloon. The balloon carries the rocket up to where the air is less dense, then the rocket fires and breaks away. How does the rocket know when to fire?"

"Two ways. A barometric switch can be installed that will act at a certain alt.i.tude, or a signal can be sent from the ground."

"The antenna," Scotty said. "It can send a signal."

"Sure."

"I'm with you all the way, until you say this shows why the stingarees fly. Why send up rockoons? What's the reason?"

Rick forgot he was holding a coffee cup and waved his hand. He recovered in time to keep from spilling the hot liquid on Steve's rug. "Scientific research is usually the reason for rockoons. They carry experiments."

Scotty snorted. "Are you telling me Lefty Camillion has turned scientist?"

"Nope." Rick yawned. "I take it back. We still don't know why the stingarees fly. We only know what they are. Where do you suppose Steve is?"

"That's the eighth time you've asked. He'll be here when that business of his is over."

The telephone rang. Rick jumped to his feet and beat Scotty to the phone only because he was four steps nearer. "h.e.l.lo?"

An unfamiliar voice spoke. "Stay away from the creek, and stay away from the house. If you don't, your crab-catching buddy is going to be turned into crab food." The line went dead.

Rick turned, eyes wide. Suddenly he was no longer sleepy. "Did you hear that? He said to stay away from the creek and the house, or our crab-catching buddy would be turned into crab food!"

"He must have meant Orvil Harris!" Scotty exclaimed. "Rick, let's get going!"

The boys started for the door at a run, but Rick stopped as his eye caught the rocket. "Check the gas," he told Scotty. "Steve has a spare can in the workshop. The runabout tank must be getting low. I'm going to hide the rocket."

Scotty left at a run. Rick picked up the rocket and surveyed the scene.

Where could he hide it? He hurried into the kitchen and examined the cabinets, then shook his head. Too obvious.

The refrigerator caught his eye. An ap.r.o.n at the bottom concealed the motor unit. He knelt and pulled the ap.r.o.n free from its fastenings.

There was room next to the motor--unless the heat of the motor caused the rocket fuel to burn. He opened the refrigerator and examined the control, then turned it to "defrost." It wouldn't go on until they got back. Hurriedly he put the small rocket in at a slight angle. It just fit. He snapped the cover back in place and ran to join Scotty, who was already in the boat.

"Gas okay," Scotty called. "Let's go."

Rick cast off and jumped aboard. Scotty started the motor and backed into the stream, then turned sharply and headed toward the river.

Neither boy spoke. Their sleepiness was gone now, forgotten in their fear for Orvil.

Scotty held the runabout wide open, at its top speed of nearly twenty miles an hour. They sped across the Little Choptank River straight for Swamp Creek, with no effort at concealment.

Rick saw a low, white boat some distance down the river and grabbed Scotty's arm. "Isn't that Orvil's boat?"

Scotty looked for a long moment. "It looks like it. Let's go see."

They swung onto a new course, in pursuit of the white boat. It might not be Orvil's, but it was like it. Both boys could now recognize the design characteristic of boats built on the Chesapeake Bay. The boats were known as "bay builts," and distinguished by their straight bows--almost vertical to the water line--square sterns, and flaring sides. The design was ideal for the shallow, choppy waters of the bay, and the boats could take a heavy bay storm with greater comfort and safety than most deep-water models.