ahead of the pistol grip. Scotty had deliberately fired ahead of the propeller, knowing that the wire leader would be caught and would wrap around the shaft.
Rick saw the spear stop short as the wire caught, saw it hauled back against the propeller and drop free as the prop blades cut it loose. Scotty shot up for a breath, then dove instantly, toward the rapidly falling spear.
Rick had to breathe himself. He surfaced, caught a quick breath, then went under again. Scotty was picking up the spear. Rick saw him place it in the gun barrel, swing the loader over the razor-sharp harpoon head, and shove down on the spring. In a moment the gun was loaded again. Luckily the spear had not bent when the prop blade hit it.
The boat had come to a halt, the engine dead. The propeller could no longer turn against the wrapping of wire and heavy fishline. Scotty hooted twice, their signal to surface, and Rick followed him up. Near the surface they separated, Rick taking the side of the boat away from his friend. He longed for a weapon, even a hand spear. But he was helpless. Scotty would have to get in the first blow with the gun. But, Rick thought, that might give him time to get over the gunwale to grapple with the shadow.
His head broke water. He pulled the snorkel from his mouth and let it hang. As luck would have it, the shadow saw him first. He stood up, oar in hands, poised for a swing at Rick's head.
Scotty's voice stopped the swing. "Don't do it or you'll get three feet of steel through you!"
The man turned and faced the needle point of Scotty's spear. The oar dropped from his hands.
Rick gulped his relief. Apparently the shadow had no weapon.
"Jump overboard!" Scotty ordered.
The man hesitated. Scotty thrust the spear gun forward. "Jump, I said!"
The shadow did, and sank in a flurry of bubbles. When he rose to the surface again, the point of the spear was against his back. "Hang on to the boat with both hands," Scotty directed.
Rick got to his side with a kick of the flippers and ran his hands over the man's clothing. He found a switch knife, which he put in his belt. "He's clean," he said. "No other weapons."
"Take a look in the boat," Scotty suggested.
Rick did so, lifting himself up on the gunwale. There was nothing in the boat but oars and a can of gasoline.
"Want to tell us why you tried to run us down?" Rick asked.
The shadow merely stared.
"Talk," Scotty ordered, "or I'll put this spear through you."
The man spoke, and his accent was the soft speech of the island. "No, you won't. I could explain running down swimmers by accident, but you could never explain putting a spear through a man in a boat. You don't want that kind of trouble."
Scotty grinned at the truth of it. "Okay," he said. "Just one thing. Don't push us too far. Stay in the water until we're ashore, and don't try to overtake us."
"Better heed that advice," Rick warned. "Come on, Scotty. Let's go." He put his snorkel in place.
Scotty moved to his side. "Welcome to the hospitable waters of St. Thomas," he said. "What say we look up some friendly sharks before we go ashore?"
CHAPTER IV
Visitors by Night
Rick and Scotty stood on the pier and watched their erstwhile shadow row slowly toward another pier some distance away.
"We probably should have tied him up and called the police," Rick remarked.
"It wouldn't have gotten us anything," Scotty disagreed. "He could always claim he didn't see us in the water. After all, it wouldn't be the first time divers had been run over by motorboats."
"It's too late now, anyway. Let's dress, then go to the hotel and tell Zircon and Tony about this."
As they dressed in the small cabin of the Water Witch, Rick spoke aloud the question that had been bothering him. "What did he have to gain by running us down? That's what puzzles me. It was a stupid thing to try, because he didn't really have much chance of getting both of us, or even one, once he failed to catch us by surprise."
"He wasn't very well prepared for murder, either," Scotty added. "No weapons except a switch knife."
Rick nodded agreement. "He was desperate," he concluded. "Suddenly he had to take a chance on getting us. He must have known it wasn't much of a chance. Either he lost his head, or he wasn't very bright. What could have made him try?"
Scotty had no answer, nor could Rick even hazard a reasonable guess.
They locked the cabin of the Water Witch, walked into town, and found a taxi. Their shadow did not show up again, and if a new tail had replaced him, the new one was too good to be spotted. However, the boys doubted that they were being followed.
"I just don't get it," Rick said for the twentieth time. "Our friend must have lost his head. Otherwise he'd have waited on shore and continued to follow us when we came out of the water."
"We'll probably never know," Scotty returned. "After all, we'll be gone in the morning."
"I know. But meanwhile, we'd better have eyes in the back of our heads."
The taxi discharged them in front of Alexander's Rest and they climbed out and surveyed the hotel with interest.
Scotty spoke first. "Alexander's Rest? Which Alexander? The Great, or Hamilton? If it was Hamilton, as Dr. Ernst said, he must have built it personally."
It was a two-story frame structure that had definitely seen better days. On closer inspection Rick decided that the second story had been added as an afterthought. It looked like the second layer of a poorly constructed cake.
Inside, however, the hotel proved to be very comfortable. It was cool, and the rooms were large and clean. The boys learned that they had been registered in a twin bedroom on the second floor, while Zircon and Briotti were on the first floor.
The boys found the scientists attired only in shorts, cooling off over long, cold drinks. They accepted glasses of iced ginger ale and told the scientists of their adventure.
"It's amazing." Tony Briotti shook his head. "Do you realize that you two are a phenomenon? I should write you up for one of the scientific journals."
"You mean because we turned the tables on the shadow?" Scotty asked.
"No. Because you're adventure-prone. Did you ever hear of people who are accident-prone?"
Zircon chuckled. "A good observation of these two. I agree absolutely, Tony. They are adventure-prone."
Rick sighed. "All right. What's the joke?"
"None. I'm quite serious." Tony found more ice for his glass. "Insurance statistics show that certain people are accident-prone. Accidents happen to them. They're going along minding their own business and bang! A streetcar jumps the tracks and hits them. Or they step into open manholes. They're the kind of people who always manage to be walking under things when workmen drop tools."
"And you," Zircon concluded, "are adventure-prone in the same way. Consider this. Had you walked down the street either a minute earlier or later this morning you would not have
