the shadowy figure which had entered the Mead home carried a large package under his arm. He deposited it in the library fireplace, mumbled a few indistinct words, and stepped back.

The detectives and John Mead waited. To their disappointment the fellow did not touch the paneled wall. Instead, he tiptoed toward the hall door.

Mr. Hardy stepped from hiding and pinned the man's arms behind him. Startled, the stranger tried to wrench himself free, but was confronted by two more detectives. A flashlight was focused on his face.

Mike Matton! Mr. Hardy identified the fellow at once from a description Frank and Joe had given him of the dishonest locksmith.

"I ain't denyin' it," Matton said. "Take your hands off mel"

"What are you doing here?" Mr. Hardy demanded.

195.

196 "I could ask you the same question," the fellow replied with a sneer.

"Open that package!" the detective ordered him.

At first Mike was inclined to be insolent and not obey. When he was told the police were looking for him and it would go still harder with him if he did not tell the truth, the fellow changed his mind. He pulled the string from the bundle in the fireplace and several fine door knockers rolled out.

"Where did you get these?" Mr. Hardy asked him.

"I ain't sayin'."

Under grueling questioning, however, Ben Whit-taker's former a.s.sistant admitted he had stolen them. He told a story of being in debt from gambling and of having taken this means to pay his bills.

"I know a guy who collects these things," he said. "And as soon as he comes he's goin"

to pay me a lot of money for them."

Mr. Hardy asked how soon the man would come. At this the fellow became frightened, and said he hadn't meant that. He became so confused, Mr. Hardy could not be sure what the true story was.

"Give me the key you used to get in here!" the detective demanded.

Matton refused to do this, so he was searched and the key taken from a pocket. It was new. Under questioning the thief finally said that a stranger had brought the original to Ben Whittaker's shop to have a duplicate made. The key was so unusual Mike had made one for himself as a keepsake. Mr. Hardy doubted this story but could get nothing further from the young man.

"Where's the secret panel?" he asked suddenly.

Mike Matton looked blank, and the detective was convinced the man knew nothing about it. He ordered one of his a.s.sistants to take the fellow to Police Headquarters. Matton put up a struggle, but handcuffs were clapped on him and he was driven to town.

Mr. Hardy continued his search for a magnet. It was not long before his keen eyes detected the loose floor board. Hopefully he raised it. To his relief the magnet lay beneath.

It was only a matter of moments before the famous detective had the secret panel revolving. He leveled the beam of his flashlight into the mysterious room beyond, and breathed a prayer of thankfulness.

"Dad!" Frank and Joe cried in unison.

Mr. Hardy had steeled himself never to show emotion in public. But he was so relieved to see his two sons and Chet Morton unharmed that he hugged each of them in turn. A moment later, however, he regained his composure. He spoke to Miss Johnson, who thanked him for rescuing her.

"This is Lenny Stryker," Frank introduced the youth on the cot.

The young man, whose condition had improved vastly during the morning, sat up. "I hope you ain't going to arrest me, sir. I ain't a thief," he said.

"Don't try to talk, Lenny," Frank said kindly. "We'll tell Dad your story."

198 The Hardy boy retold Lenny's experiences as he had given them a little while before.

The fellow's uncle had asked him if he would like a job and earn some money to help his mother. But the boy had been tricked.

After being introduced to several other men, Lenny realized they were about to rob a museum. He had wanted to have no part in it but had been forced to go along. The youth had been so nervous he had been unable to do his share of the work; this had been to take away the guard's gun, and because of his mistake, Lenny had been shot.

"I can't understand," Mr. Hardy said to him, "why your uncle should want an inexperienced person along on such a job."

"I guess he was trying to get square with my mother," the young man told him. "He's my father's half brother and wanted to marry my mother. But she didn't like him and now I can see why. I guess she knows he ain't on the level."

The boy revealed that his uncle had a clever instrument which he used in robberies; a device which would open locks and silence burglar alarms. It was not a key, Lenny said, but he did not know exactly what the gadget was.

"My uncle bragged that he invented it," the youth concluded his story.

Mr. Hardy nodded. "That explains a great deal," he said, then asked suddenly, "Is your uncle Whitey Masco?"

"You know?" Lenny cried out in alarm. "Oh, please, Mr. Hardy, don't send me to jail!"

"I'm not going to send you to jail, Lenny. As a matter of fact, I'm going to send you home to your mother. But I shall get that uncle of yours behind bars just as fast as I can. You can help me by telling everything you know about Whitey Masco."

Lenny could tell little. He had no knowledge of his uncle's personal life, and most of the boy's harrowing experience after being shot was known already. It was purely accidental that he had overheard Masco say, "We better hide the kid behind the secret panel." Left alone for a few seconds in a house to which he had been taken temporarily, Lenny had dragged himself to a telephone and called his mother.

"It's very lucky for us you did that," Mr. Hardy told him. "And now, Mack," he added, turning to one of his men, "take Lenny and Miss Johnson to the Stryker home." To the nurse he said, "Martha, would you mind going on from there to my house and telling the folks what has happened? a.s.sure them we're all right, but the boys and I still have a job to do here and we may not get back for several hours."

Frank and Joe offered to carry Lenny to the waiting car, but their father held them back.

It would be wiser if they did not show themselves outside. With so many people coming and going, spies in the garden might become confused and think no one was 200 left in the house. And that was just what he wanted.

"But what are we going to do here, Dad?" Joe asked.

His father smiled. "Follow a hunch of your brother's," he said. "Frank whispered to me a while ago that he'd like to stay and do some special investigating."

The detective directed Mack to flourish Mike Matton's key for the benefit of anyone who might be outside, and make a great ceremony of locking the door.

"Come back here with another car," the boys' father directed him, "but park it along the road beyond this property."

After they had gone, Mr. Hardy turned to Frank and said he was ready for the investigation. His son led the way to the paneled wall in the secret room, pushed aside the bird's wing, and showed his father the three slits which formed the strange Y symbol.

"We tried to discover what to do with them, but we had no success," Frank said. "Can you tell us anything about them, Mr. Mead?"

The man shook his head. He reiterated his former statement of knowing nothing about the secret devices in the elder John Mead's home. "The whole thing is a great mystery to me," he said.

Mr. Hardy was staring at the unusual ring on the man's finger. Now he asked Mr. Mead to take it off so that he could examine it. Obligingly John Mead handed over the ring, and watched eagerly as the deThe Capture 201 tective took a magnifying gla.s.s from his pocket and studied the strange Y insigne.

Suddenly Mr. Hardy smiled broadly and moved something with his fingernail. To the amazement of the onlookers the top of the ring raised up on a tiny hinge. Beneath it lay the three pieces of a miniature key in the shape of the Y symbol.

Mr. Hardy picked up the key and set the three p.r.o.ngs at right angles to the diminutive handle. Quickly he inserted the key into the slits on the wall and in a moment pulled open a small door.

The others gasped. Within the opening beyond lay bits of exquisite and rare jewelry. Mr.

Hardy recognized them at once as objects stolen from the museums.

"Loot!" Frank yelled.

"Yes," his father agreed.

Joe's sharp eyes had spied a piece of paper lying on the floor of the little safe. He picked it up and read aloud: This device must never be used. Upon my death I ask that it be given to the F. B. I.

John Mead Young Mr. Mead stared in blank amazement. "But there's no device here," he said.

"What could my uncle have meant?"

"I believe that is easily explained," Mr. Hardy told him. "Your uncle was an inventor. His main 202 interest was in locks and keys. He probably figured out a gadget which could open any lock without the use of a key."

"But how could there be such a thing?" John Mead asked.

"Wonderful things are being done these days in the field of electronics," Mr. Hardy explained. "Your uncle's device may work by radio beam, or he may even have figured out some combination of metals which make a new and powerful magnet."

"Do you think he destroyed it before his death?" Mr. Mead asked.

"Indeed I don't," the detective replied. "I think Whitey Masco stole it. That is the device the thief has been using to get into museums!"

John Mead was silent a moment. Then he inquired how the crook could have made a key similar to the one in the signet ring. Mr. Hardy told him about the duplicate which had been stolen from a museum.

"I believe the fellow is wearing it," he said. "It's possible your uncle knew about the one in the museum, and being interested in clever ideas, copied it. There are many bits of the story still to be filled in. Our job now is to locate Whitey Masco. Then we can get the rest of the details."

"How are you going to capture him?" Joe asked his father.

Mr. Hardy admitted he had not formulated a plan of action as yet. He was afraid the crook, knowing the police were hot on the trail, might go into hiding again for a long time.

Suddenly Frank gave a yell. "I have it!" he cried. "We'll capture that guy tonight!"

The others stared at him, unbelieving.

"Tell us your idea!" Joe demanded eagerly.

CHAPTER XXV.

The Key to the Mystery.

the three Hardys and John Mead waited inside the dark mansion. It was nearing midnight, and so far nothing had happened. But Frank was sure his hunch was right; that Whitey Masco would return to the Mead home for his treasures and take them away in a recently purchased underwater boat.

"He probably knows some secret entrance to this place, even an underground pa.s.sage, and will be able to sneak in without being seen. Masco will figure he has nothing to worry about, but we'll nab him!"

Frank and his father were posted in the inner room behind the secret panel, which was now closed. Joe and Mr. Mead had hidden behind furniture in the library. The four men had fortified themselves against hunger by eating some concentrated food tablets Mr. Hardy always carried with him.

Suddenly there came a barely perceptible sound in the hall. A moment later Joe was sure a third person had entered the library. But the phantom figure moved in complete darkness.

204.

205 A slight thud. The unseen man must be removing the floor board which covered the magnet. A few seconds later there was a slight change of air. Joe was positive the intruder had opened the secret panel.

In the inner room Mr. Hardy and Frank were tense. They had hidden in a corner of the room. Now they knew someone had opened the secret panel and was moving on tiptoe across the room.

The place was in inky blackness, and for several moments there was not even the sound of anyone breathing. Frank and his father had just concluded the intruder had gone out again, when their ears caught a faint thump. The man must have laid down the magnet.

Again silence. Was he trying to open the wall safe? Then the Hardys caught a tiny ray of light shielded in a cupped hand. It gleamed on the three slits under the bird's wing. From the darkness came three p.r.o.ngs to fit them.

The safe opened. The unseen man uttered a low curse. Mr. Hardy pressed Frank's arm, then jumped the fellow while the boy snapped on his flashlight. There was a slight tussle as the detective took the man's gun from him.

"You got him!" Joe cried, leaping through the doorway.

"Yes, I have Whitey Masco at last," Mr. Hardy replied grimly. "A long-wanted criminal who will commit no more robberies, nor send me threatening letters. Feel like talking, Whitey?"

206 The prisoner flashed looks of hate at the detective and his sons. He knew them, but gazed at Mr. Mead without recognition.

"Another d.i.c.k?" he asked.

Mr. Hardy shook his head. "This is Mr. John Mead who owns this house."

Whitey sneered. "John Mead's dead." Then he added, "He was a clever old man, but I guessed his secrets."

"You knew my uncle?" Mr. Mead asked in astonishment.

"So he was your uncle, eh? Sure I knew him. Met him on a train once and got myself invited here," the crook bragged.

Now that he had started talking, Whitey could not resist the temptation to boast. He told how "the old man" had revealed perfecting a device with which a person could commit the perfect crime. The inventor had said it was well hidden and never would be used.

"But I found it!" the thief gloated.

Suddenly Whitey realized he had talked too much. Mr. Hardy had been waiting for this.

He went through the man's pockets, and in vjne of them found a small device which looked like a miniature radio. When a small lever on it was pressed, a long magnetized needle shot out.

"Was that my Uncle John's invention?" Mr. Mead gasped. "The gadget which can open any lock and silence burglar alarms?"

207 "Yes," Mr. Hardy replied. "And the F. B. I. will be very very interested in it. Suppose you and I interested in it. Suppose you and I run down to Washington and present it to them, Mr. Mead."

During this conversation Whitey had been edging toward the secret panel. Suddenly he made a dash through the opening. But Frank and Joe were on him in a second.