"All right," she said. "Come on in."

The woman explained that she never unlocked the door to strangers until her helpers came, because she once had been robbed while alone.

"You know," she said, "everybody eats, even thieves. I have to be careful who I let in."

62 She prepared a delicious meal for the boys, while they looked around. They saw everything, even the bas.e.m.e.nt, for the woman proudly showed them her preserve closet.

There was nothing the least bit suspicious in the house. As the boys were driving away some time later, Chet, almost too full to speak, congratulated Frank on his cleverness in getting them into the roadside restaurant.

"Only our stop there didn't net us anything except a good meal," the Hardy boy reminded him.

He drove back to the humming traffic light, then headed in a westerly direction. At the end of ten minutes, the boys came to a ball field. They returned once more to the signal, and Joe pointed out that the easterly direction would take them directly to the bay.

"Our last chance to find out where Doctor Lyall was taken is to drive south," Joe remarked.

As they reached a congested business section of Bayport ten minutes later, Frank suggested they separate. "Joe, suppose you take this avenue. I'll go over to Wallace. Chet, how about you taking Ferry Street?"

Chet started off enthusiastically, but after being shooed out of a laundry, icily dismissed from a beauty parlor, and practically thrown out of a soda bottling factory, he was ready to quit. He walked back to the car. Joe, who had had no better luck, was waiting for him.

68 "Frank must be on a hot trail," Joe decided, when half an hour went by and his brother had not returned.

At that very moment Frank was hiding in the dimly lighted cellar of a warehouse. He had fol-lowed a tip given to him by a small boy that rough-looking men had been seen going to and from the warehouse with odd-shaped packages at all hours of the day and night.

Frank was watching a man who had just stepped from a freight elevator. Reaching the far wall of the cellar, the operator leaned down and evidently worked a catch. A large door slid open and the man disappeared beyond it. He returned almost immediately, however, closed the door, and went back to the elevator.

Frank Hardy came out of his hiding place and approached the mysterious sliding door.

He found the catch, and slowly pushed against it with his knee. The door opened. The place beyond was in total darkness.

Whipping out his flashlight, Frank turned its beam on the mysterious room. Then he muttered in disgust, and quickly making his way from the building, returned to the car.

"Did you find anything?" Joe asked him eagerly.

"Yes. A huge refrigerator! It was empty except for the elevator operator's lunch!"

The others laughed when Frank related how he 64 had thought Lenny Stryker was hidden in the warehouse, and the elevator operator was taking food to him.

"So I investigated, but found nothing more suspicious than an icebox," he concluded.

"Golly, that reminds me. I have to buy some meat to take home," Chet said, looking at his watch. "I'd better go. That is, if you're through work," he added.

Frank sighed. "The humming signal clue seems to have petered out," he declared. "I guess there's no use doing any more about it now."

The Hardys offered to drive Chet home, but he insisted on taking the bus. He said good-bye to the brothers, who headed for home. Joe had an idea.

"It's still early and I'm fearfully hot, Frank. What say we go for a swim and combine a little business with pleasure?"

"What's on your mind?"

"How about diving for Mr. Mead's key?"

"Swell. We'll stop at the house and get our suits."

Frank parked the car in front of the Hardy home instead of going into the garage. Aunt Gertrude, sitting in the porch swing, remarked about this at once. She wanted to know where the boys were headed, and why. Joe's reply that they were working on a mystery satisfied her for the moment. But when they could not find their swim trunks, and had to ask Miss Hardy about them because their mother was out, she eyed her nephews distrustfully.

65 "Whoever heard of solving a mystery in a bathing suit!" she scoffed. "I declare, what excuses boys won't think of nowadays!"

"Didn't boys used to think?" Joe asked mischievously.

"You know what I mean, Joe Hardy, and don't try to pull the wool over my eyes. You're not going to solve a mystery, you just want to go swimming. Why didn't you say so in the first place? Well, I have other plans for you."

The boys wilted. They knew from experience that their aunt probably was going to ask them to clean up their workshop or go on some errand for her.

"Please, Aunty," Frank pleaded, "we aren't going swimming for pleasure. There's a clue to a mystery at the bottom of Barmet Bay. It's very necessary that we do some diving and try to find it."

Aunt Gertrude sniffed, unbelieving. "Sounds funny to me. What is it you want to dive for?"

"A key."

Miss Hardy fixed a steady eye on her nephews. It is doubtful that she ever would have told them where their bathing suits were. Luckily, their mother returned at that moment and found their trunks.

Frank drove to the boathouse where the Sleuth Sleuth was tied up. He and Joe hung their was tied up. He and Joe hung their clothes on hooks, donned their trunks, and headed the Sleuth Sleuth out into Barmet Bay. It took out into Barmet Bay. It took the boys some time to 66 locate the spot where Chet's ill-fated boat had gone down.

"I'll go over first," Frank offered.

He made a clean, deep dive from the stern of the Sleuth. Sleuth. Joe watched the spot where Joe watched the spot where his brother had gone down. When more than a minute went by and there was no sign of Frank, he became concerned.

Joe leaned far over the side of the boat and looked down through the water. Then he stood up and studied the surface of the bay. His brother was not in sight. The boy's heart began to pound in terror.

What had happened to Frank?

CHAPTER VIII.

The Curious Symbol.

joe hardy dived into the water. He went straight to the bottom. Then, hoping against hope, the worried boy looked around for his brother.

Where was Frank?

Swimming under water until he thought his lungs would burst, Joe finally had to come to the surface. He looked around. Still he did not see Frank. Sick at heart, he climbed into the Sleuth and again gazed about him. and again gazed about him.

Suddenly his pulses quickened. Weren't those two arms he saw at a distance, alternately cleaving the water? As the swimmer drew closer, Joe could see his head. Frank!

Panting, the older boy grabbed at the side of the boat.

"Gee, I'm glad you're okay," said Joe. "You gave me an awful scare. I went down to look for you. Where've you been?"

"I-saw-a-whale!" Frank gasped.

"A whale? Never heard of them in Barmet Bay," Joe said, astounded. Then, after helping Frank aboard, he added with a grin, "Did he swallow you? You stayed away long enough!"

"Don't-blame-you-for thinking so," Frank replied.

He went on to say that he had noticed the whale, or perhaps a submarine, making great speed through the water some distance away.

"What were you doing so far from here?" Joe asked.

"The dory below us isn't Chet's," his brother told him. "So I swam around trying to find it.

Guess I came up for air when you dived for me. I went farther than I realized. Sorry I worried you."

"Forget it. Did you see the Bloodhound?" Bloodhound?"

"No, but I'm sure it's somewhere near here."

Joe started the engine of the Sleuth. Sleuth. Frank gazed down through the water as they made Frank gazed down through the water as they made way slowly. No sunken boat was visible.

"Guess we'll have to give it up," he sighed. "Well, no one can say we didn't try. I sure wish I hadn't lost Mr. Mead's key. If he should-hey, hold it, Joe!"

"See something?" Joe cut the motor.

Both boys leaned over the side of the Sleuth. Sleuth. Below them, on the bottom of Barmet Below them, on the bottom of Barmet Bay, lay a dory. It was impossible from the surface to identify it as Chet's, but hopefully Frank dived into the water. Half a minute later he reappeared, reporting that it was indeed the Bloodhound, but that he had not found the lost key. but that he had not found the lost key.

69 "I'll take a try," Joe offered.

He had no better luck. After talking the matter over, the brothers concluded that they would never find the key in this. .h.i.t-and-miss manner, so they proceeded to map out a scheme for the search. It was decided that Frank would hunt around the fore part of the sunken dory, while Joe would take the aft section.

"Then we'll try midships and the engine," the older youth suggested.

The brothers took turns. Their first endeavors brought no results, and Frank's attempt at the middle part of the Bloodhound Bloodhound did not yield the key, either. The boys knew that if it had did not yield the key, either. The boys knew that if it had fallen into the sand there would be no chance of finding it. The area around the engine was their last hope. Joe shot down through the water and grasped the flywheel of the dory's motor. Feeling around quickly with his free hand, he came upon something wedged tightly between the engine and a crossbeam. Pulling it out, he swam quickly to the surface.

"You found it!" Frank yelled excitedly.

It was the missing key, indeed. Joe was all for going at once to the Mead house to try it, but his brother reminded him they had promised their father they would not enter the place without a police escort.

Joe was impatient, but agreed with Frank. He suggested they hurry back at once for their clothes, find their father and see if he would change his mind*

70 Frank, however, continued to gaze down through the water.

"I think I'll dive in once more," he said. "I'm sure the fellow who took Chet's good money for that old tub down there isn't going to show up with the owner's papers. Maybe we can find some identification on the boat."

"Good idea," Joe admitted. "You swim along one side, and I'll take the other. Suppose I go first."

Joe found nothing, so Frank went over. A few seconds later he came to the surface, his eyes shining.

"A mark is carved on the gunwale," he said excitedly. "It looks exactly like that strange open-faced Y we saw on John Mead's ring!"

"Honest?" Joe yelled. He was over the side in a flash to look at the crudely carved mark himself. He came up, climbed into the Sleuth, Sleuth, and started the motor, saying they must do and started the motor, saying they must do something about this clue at once.

"But what?" Frank asked. "From Chet's description I'm sure the man who sold him the boat isn't the same person we met on the road. Remember, Chet said he was a stocky man of thirty who didn't smile. That doesn't fit John Mead."

Joe had to admit this was true. But the boy longed for action of some kind, and sent the Sleuth skimming across the water at a fast clip. Reaching the boathouse, he scrambled into skimming across the water at a fast clip. Reaching the boathouse, he scrambled into his clothes, urged Frank to hurry, and then drove home at once. He immediately went to the telephone and called Chet 71 Morton to ask him if he had heard from the former owner of the Bloodhound. Bloodhound. The stout The stout boy ruefully admitted that he had not.

"I'm afraid I got gypped," Chet said sadly. "So you fellows will have to keep on looking for him."

"We?" Joe exploded. "What's the matter with Joe exploded. "What's the matter with you?" you?"

"Well, what's the use of having friends if you can't call on 'em for help once in a while?"

Chet asked.

"Okay," Joe laughed. "I just wanted to be sure you still needed us. We picked up a clue for you."

"You did?"

Joe told about the odd mark on the dory, and the fact it seemed to be the same as the Y on John Mead's ring. Chet was amazed, but could not figure any connection. He confirmed the fact the fellow who had sold him the old dory and John Mead could not be the same person.

"But maybe they both belong to the same secret society, and the funny Y is their insignia," Chet suggested.

"Maybe," agreed Joe soberly.

He had hardly hung up the telephone when it started to ring. It was a long-distance call from Mr. Hardy. The detective said he would not be hom

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"How are you boys making out?" he asked.

Joe related the day's events, admitting that, up to the moment, the clues they had run down had 72 brought no results. His father took a different view, however, saying the elimination of false clues was a battle half won.

"Don't be discouraged, son," he advised. "And ask Chief Collig for permission to go into the Mead house alone if he can't send a man with you. I venture to say if you keep trying you'll find a keyhole somewhere. And now put your mother on the wire."

The boys waited until Mrs. Hardy had finished speaking, then told her where they were going. She asked her sons to be home by dinnertime.

"We'll be back by then," the brothers promised.

They went off in their roadster, drawing up in front of Police Headquarters several minutes later. Chief Collig, just coming out, walked up to them and started speaking at once.

"No, there haven't been any new crimes reported," he said briskly. The Hardys thought they detected a note of sarcasm in his voice. "Not a thing. No more doctors kidnaped, no hardware thieves caught."

"Oh!" said both boys. Then Frank grinned and added, "We've come to ask you a favor."

Collig was supicious, but he relaxed when they told him of their desire to visit the Mead premises. The Chief said he could not spare any men to accompany them, but that it would be all right for the boys to go alone.

73 "But how are you goin' to get in?" he asked. "Riley said there weren't any keyholes at the house. Queer place, I'd say."