"On this small radio phone. A pair of receivers tuned to the right wave-length are in my diving helmet, and I will be able to hear you although I can't reply. I won't be gone long: I have only a small air tank, large enough to keep me going for thirty minutes. Now help me into my suit and keep a sharp watch. A timely warning may save my life if anything happens."

With Carnes' a.s.sistance, Dr. Bird donned a deep-sea diving outfit and screwed down the helmet. He crawled through the inner door into the lock and lifted the inner door into place. Carnes fastened the door with nuts and the Doctor opened a pair of valves in the outer door and filled the lock with water. He removed the outer door; and, taking in one hand a steel-shod twelve-foot pike with a hook on the end, and in the other a waterproof flashlight, he sallied forth. As he left the sh.e.l.l he paused for a moment, and then returned and picked up the heavy wrench with which he had removed the nuts holding the outer door into place. He fastened the tool to the belt of his suit. Then, with a wave of his hand toward the detective, he approached the hulk.

The hole in the side was too high for him to reach, but he hooked the end of his pike in one of the joints of the _Arethusa's_ plates and climbed slowly and painfully up the side of the vessel. As he disappeared into the hull, Carnes realized with a sudden start that he had been watching his friend and neglecting the duty imposed on him of keeping a sharp watch. He turned quickly to the floodlights and searched the sea bottom.

Nothing appeared, and the minutes moved as slowly as hours should.

Carnes felt that he had been submerged alone for weeks, and his nerves grew so tense that he felt that he would scream in another instant. A sudden thought sobered him like a dash of cold water. If he screamed, Dr. Bird would take it for an alarm signal and possibly be afraid to emerge from the vessel. His watch showed him that the Doctor had been gone for twenty-five minutes and he moved slowly to the radio transmitter.

"Dr. Bird," he said slowly and distinctly, "you have been gone nearly thirty minutes. Nothing alarming has appeared but I will feel better when I see you coming back."

He glued his eyes on the opening in the ship's side and waited. Five minutes pa.s.sed, and then ten, with no signs of the Doctor. Carnes moved again to the receiver.

"It has been over half an hour. Doctor," he cried in a pleading voice.

"If you are all right, for G.o.d's sake show yourself. I am frantic with worry."

Another five minutes pa.s.sed, and the sweat dripped in a steady stream from the detective's chin. Suddenly he gave a sob of relief and sank back against the side of the globe. A bulky figure showed at the edge of the hole, and Dr. Bird climbed slowly and heavily out of the hold and dropped to the sea bottom. He lay p.r.o.ne for a moment before he rose and made his way with evident effort toward the sphere. He entered the compartment and with a heroic effort lifted the outer door into place, and feebly and with fumbling fingers placed nuts on the bolts. His hands wandered uncertainly toward the valves and closed the upper one. He waved his hand toward Carnes and sank in a heap on the floor of the lock.

With trembling hands Carnes connected the air and opened the valve. Air flowed into the lock and the water was gradually forced out. When the lock was empty, he waited for Dr. Bird to close the outer valve but the Doctor did not move. Carnes tore at the bolts which held the inner door and threw his weight against it. It held against his a.s.sault, and he thought frantically. An inspiration came to him, and he disconnected the air valve. With a whistling rush, the air from the lock rushed into the sphere and he forced open the inner door. A stream of sea water drove against his feet through the open valve, and he reached for the valve to close it. The force of the water held it open for a moment, but he threw every ounce of his strength into the effort. The valve slowly closed.

It was beyond his strength to haul the heavy Doctor with his pressure diving suit through the restricted confines of the inner door, so Carnes wormed his way into the lock and with trembling fingers unscrewed the helmet of the Doctor's diving suit. The helmet clanged to the floor and Carnes scooped up his hands full of water and dashed it into the Doctor's face. There was no response and he was at his wit's end. He sprang for the radio to order the sphere hauled up when his glance fell on the oxygen tank. It took him only a moment to connect a rubber hose to the tank, and in a few seconds a blast of the life-giving gas was blowing into the scientist's face. Dr. Bird gave a convulsive gasp or two and opened his eyes.

"Shut off the juice, Carnes," he said faintly. "Too much of that's bad."

Carnes shut off the oxygen and Dr. Bird struggled to a sitting position and inhaled deep breaths.

"That was a narrow squeak, old dear," he said faintly. "Give me a hand and I'll climb in."

With the detective's aid he climbed into the sphere and Carnes fastened the inner door. Slowly the Doctor rid himself of the diving suit and lay p.r.o.ne on the floor, his breath still coming in gasps.

"Thanks for your warning about the time, Carnes," he said. "I knew that my air supply was running short but I was caught down there and couldn't readily free myself. I thought for a while that my time had come, but it wasn't so written. By the looks of things, I freed myself just in time."

"Did you find out anything?" asked the detective eagerly.

"I did," replied Dr. Bird grimly. "For one thing, the gold is no longer in the hold of the _Arethusa_."

"It's gone?"

"Clean as a whistle, every bar of it. A hole has been cut in the vault around the combination, and the bars slid back and the door opened. The gold has been stolen."

"Might it not have been stolen before the vessel sank?"

"The idea occurred to me of course, and I examined things pretty carefully. I know that the theft occurred after the vessel sank."

"How could you tell?"

"For one thing, the hole was cut with an under-water cutting torch. For the second, look here."

The Doctor rolled up his trousers and showed the detective his leg.

Carnes cried out as he saw huge purple welts on it.

"What caused that?" he cried.

"As I entered the vault, I stepped full into a steel bear trap which was set there for the purpose of catching and holding anyone who entered.

Someone has visited the _Arethusa_, since she sank, and looted her, and also arranged so that any diver who got as far as the vault would never return to the surface to tell of it. Luckily for myself, I carried a heavy wrench and was able to free myself. Most divers don't carry such a thing."

"But who could have done it?"

"That's what we have got to find out, and we aren't going to do it down here. Give the word to have us hauled up; and, Carnes, don't mention anything about the looting of the vessel. Allow it to be understood that I couldn't get into the hold. We'll head back for New York at once. I want to have a few small changes made in this sphere before we use it again. While I am doing that, I want you to get hold of the Coast Guard or the Immigration Service or whoever it is that has the complete records in that case of alien smuggling, by the Young Labor party. When you get the information, report to me and we'll go over it. You might also drop a hint to Captain Starley that will stop all further attempts at salvage operations for a few days. Tell him that I'll arrange to have a Coast Guard cutter guard the locality of the wreck."

"Won't that be rather risky for the cutter?"

"I think not. The gold is gone and there is no reason to apprehend any further danger in that locality, at least for the present."

At nine o'clock next morning Carnes and Dr. Bird sat in the office of Lieutenant Commander Minden of the United States Coast Guard, listening intently to the history of the alien smuggling case. Commander Minden was saying:

"Their boats would load up and clear ostensibly for Rio de Janeiro or some other South American port, but once they were in the Atlantic, they would alter their course and head from the Ma.s.sachusetts coast. Of course, we had no right to interfere with them on the high seas, and they never came closer than fifty miles of our coast line. When they got that close, they would cruise slowly back and forth for a few days and then steam away south to the port they had cleared for. When they got there, of course there were no pa.s.sengers on board.

"We patrolled the coast carefully while they were around but we never got any indication of any landing of aliens and yet we knew they were being landed in some way. We drew lines so close that a cork couldn't get by without being seen and we even had the air patrolled, but with no results. Eventually the air patrol was the thing that gave them away.

"They had been operating so successfully that they evidently got careless and started a load off late in the night so they didn't reach the coast by dawn. A Navy plane was flying along the coast-line about twelve miles off when they spotted a submarine running parallel with the coast, headed north. It didn't look like an American craft and they went on and radioed Washington and found that we had no under-sea craft in that neighborhood. They returned to their patrol and followed the sub for a matter of thirty or forty miles up the coast, and then it turned in right toward the sh.o.r.e. The sh.o.r.e line there is rocky, and, at the point where the sub was heading, it falls sheer about two hundred fathoms. The sub ran right at the cliff and disappeared from view."

Lieutenant Commander Minden paused impressively. Carnes and Dr. Bird set forward in their chairs, for it was evident that the crux of the story was at hand.

"When the plane reported what they had seen, we knew how those aliens were being landed. The point where the sub went in gave us a good idea of the location of their base and we threw a cordon of men around and searched. A Navy sub was sent to the scene and they reported that there was a tunnel opening into the rock, about a hundred fathoms under water, running for they had no idea how far under the land. They stayed to guard the hole while we combed the land. It took us a week to locate the place, but we traced some truck loads of food and finally found it. This tunnel ran under the land for a mile and then ended in a large cave underground. The Young Labor party had established a regular receiving depot there, and took the aliens from the sub and kept them for a day or two until they had a chance to load them into trucks and run them into Boston or some other town in the night.

"Once we had the place spotted, we sent a gang in and captured the whole works without any trouble. The underground cavern had no natural opening to the surface, but one had been made by blasting. We captured the whole lot and then sealed the end of the hole with rock and concrete.

That was the end of the affair."

"Thank you, Commander; you have given us a very graphic description of it. I suppose you could find the entrance which was sealed up?"

"Easily. I led the raiding party. I forgot to mention one blunder we made. Evidently some word of our plans leaked out, for the sub which was guarding the outer end of the tunnel was called away by a radio message supposed to be from the Navy Department. It had gone only a short distance, however, when the commander smelled a rat and made his way back. He was too late. He was just in time to see the sub emerge from the hole and head into the open sea. He gave chase, but the other sub was faster than the Navy boat and it got clear away. The leader of the gang must have been on it, for we didn't get him."

"Who was the leader?"