"I dare say we could do with some air conditioning up here," Dr. Montrose apologized with an affable smile as they reached the hot, stifling loft.

Frank and Joe agreed wholeheartedly. Dr. Montrose switched on an overhead bulb, revealing an a.s.sortment of discarded articles. There were several battered trunks, a rusty bird cage, and piles of yellowing newspapers. Everything was coated with a thick layer of dust.

"No intruder has been up here or we'd see his footprints." The doctor chuckled.

Although the brothers had to agree, Frank and Joe still looked behind every piece big enough to conceal a person-or a typewriter. They found nothing suspicious.

When they returned to the second floor, Frank pointed to a latched door at one end of the hall.

"We haven't looked in there," he said.

"Just a small closet," Dr. Montrose replied casually. "No one could hide in it."

He proceeded down the spiral stair well to the first floor, with Joe following. Frank, lingering 142 behind, determined to check the closet himself.

Moving quickly down the hall, he opened the door and peered inside. The next instant a tall figure loomed up out of the pitch-dark s.p.a.ce.

Before Frank could take action, he was seized by powerful hands. The boy started to yell, then the sound was choked off by his a.s.sailant's crushing grip. The man was almost a head taller than Frank, and in the dim light of the hallway it was impossible to see his face.

Frank fought furiously to free himself. The locked pair swayed and stumbled in a wordless struggle. Then one hand of Frank's opponent grasped the boy's throat and banged his head against the closet door jamb.

The impact sent a flash of pain shooting through Frank's skull. With a groan, he blacked out!

CHAPTER XVI.

Signals.

meanwhile, Joe and Dr. Montrose had reached the first floor. It was a moment before they realized that Frank was not behind them. Then they heard sounds of a commotion upstairs.

"Hey! What's going on?" Joe cried. He ran back to the staircase and dashed up two steps at a time. The doctor followed, pantingly urging caution.

By the time they reached the second floor, the scuffling noises had ceased. Frank was nowhere in sight.

"Frank!" Joe yelled. "Hey, Frank! Where are you?"

The closet door stood ajar. Dr. Montrose switched on the hall light and Joe peered inside. The place was empty.

"He must be up here somewhere!" Joe exclaimed frantically.

143.

144 They peered into every bedroom and both bathrooms, but found no trace of the other Hardy boy. Then Joe noticed a clothes chute in one wall of the hallway and yanked it open.

"It leads down to the cellar," Dr. Montrose explained. "But surely he didn't-"

Without waiting to hear more, Joe dashed downstairs again. "Which way to the cellar?"

he shouted over his shoulder.

"Through the kitchen!" Dr. Montrose answered, hastening down the steps behind him.

Joe sped on and descended the cellar steps, pausing only long enough to flick on the light switch. The bas.e.m.e.nt was like a huge cobwebby tomb.

Only a single light bulb was working, but Joe noticed a wooden part.i.tion at one end of the bas.e.m.e.nt with the words, laundry room, in faded paint on the door. He struggled with the latch a moment, then yanked the door open.

"Frank!" he cried in mingled relief and alarm. he cried in mingled relief and alarm.

His brother lay stunned at the bottom of the clothes chute. Joe slipped one arm under Frank's shoulders and raised him to a half-sitting position. In doing so, Joe felt a sizable b.u.mp on the back of his brother's head.

Dr. Montrose had arrived on the scene by this time and hastily examined Frank.

"Frank's had a nasty blow," he murmured, "but I think he's coming around."

145 After the doctor and Joe had chafed the victim's wrists for a few moments, Frank opened his eyes and groaned.

"O-oh, my head! . . . Wh-where am I?"

"Down in the cellar, pal," Joe replied. "Take it easy for a bit, and then tell us what happened."

After collecting his wits, Frank related how he had looked into the closet and been taken off guard by his huge a.s.sailant. "Where is he now?"

"Not upstairs, that's sure," Dr. Montrose pointed out.

Joe pointed to an open window above the laundry tubs. "That's how the guy escaped.

After he dumped Frank into the chute, he must have slid down behind him and ducked out."

The doctor looked at the boys blankly. "But what did he want? There is nothing of great value in the house."

The Hardys exchanged puzzled glances. They were wondering the same thing. It occurred to both boys that the intruder evidently had some knowledge of the layout of the house.

Dr. Montrose and Joe a.s.sisted Frank upstairs and made him comfortable in a lounge chair. Here the doctor gave him a whiff of spirits of ammonia and a gla.s.s of water. In a few minutes the young sleuth felt fully recovered, except for a throbbing b.u.mp on his head.

"I think you'd better call the police, Dr. Montrose," Joe suggested.

146 "Yes, I'll do that, but it seems foolish if the fellow didn't take anything. Probably he was just a tramp who broke in to get some food. I'll take a look."

The physician hurried off to the kitchen but returned in a minute. "That was the answer, all right. The fellow took a lot of food."

Dr. Montrose dismissed the subject, then asked why the boys had come.

"On several counts, but we'll make it brief," Frank replied. "First, a friend of ours is looking for a certain kind of typewriter that isn't for sale around here. We heard that you have one."

"A typewriter?" The doctor's piercing eyes glinted with surprise. "Why, no-no indeed.

I've never thought of having one."

"Next," Frank went on, "we've been tremendously interested in what happened at Mrs.

Vel-man's home. We'd like to hear your theory on it."

Dr. Montrose smiled. "I'm afraid that I haven't any," he replied.

"But you did tell Mrs. Velman and her sister to take sleeping pills right before the robbery!"

The doctor frowned. "I do not like your insinuations," he said darkly. "I know nothing about the robbery." He suddenly arose, indicating the interview was at an end. The boys said good night and left.

As soon as their convertible was rolling homeward, Frank said, "Well, do you think our sus147 picions about the doc should be washed out?"

"No indeed," Joe declared. "I'm sure he's mixed up in this mystery somehow."

"You found something?" Frank asked.

For answer Joe reached into his pocket. "Look at this. It was on the floor in the laundry room."

He held out a gold cuff link, set with a bluish amber tiger, and on the reverse side were the Oriental characters meaning Hong Kong.

"It's the mate to the one lola found at the cave!" Frank exclaimed. "You think this is Dr.

Montrose's?"

"Could be," Joe answered. "Or at least it belonged to the man who attacked you, and he was no housebreaker. He's a pal of Dr. Montrose!"

"A long guess," Frank replied, then smiled. "But a good one. That guy could even be the safe-cracker!"

"The question is, could he be Chinese and what's Dr. Montrose's part in all this?" Frank queried.

"And I'd like to know," Joe put in, "is he one of the people interested in the Hai Hau? Hai Hau? Or, Or, if Dr. Montrose owns the cuff links, is he tied up in any way with one or another of the rival groups and why?"

"And, Joe, don't forget that Dad said the Chameleon was looking for cuff links like those we have. That could mean the owner might lead us to that man Balarat."

148 "First we must prove who the owner is," said Joe.

"I think we should check on the doctor's credentials," Frank declared.

Joe concurred. "For a starter, let's find out if that fancy diploma in his office is on the level. Let's see. It was Ardvor College."

The next morning there was just time enough for Joe to write a letter of inquiry to Ardvor College. Frank, meanwhile, phoned Chief Collig to brief him on all the Hardys' suspicions up to date regarding Dr. Montrose.

"I'll put a detail on the doctor at once," the officer promised. "Your story is amazing. And I'll get in touch with your father if you're in a hurry."

"Thanks."

Joe licked the envelope of his letter and applied an airmail and a special-delivery stamp.

"Hey, come on! It's almost ten o'clock!" Frank urged, with a glance at his wrist watch.

"We can drop the letter off on our way to the pier!"

The Hai Hau Hai Hau was ready to pull out as the Hardys arrived on the dock. They climbed was ready to pull out as the Hardys arrived on the dock. They climbed aboard and Joe went forward to help Chet with the bowlines.

Two last-minute pa.s.sengers, a husband and wife, showed up a moment later, breathless and clutching picnic bags. Biff and Frank took their fares and a.s.sisted them to embark.

"Another full boatload!" Biff beamed.

149 Frank grinned with satisfaction. "Nice going. Well, let's shove offl"

The day's cruises went off without a hitch. Secretly Frank and Joe kept wishing that they could have worked on the mystery, and radioed Aunt Gertrude several times for news. None came and finally the brothers arrived home at suppertime.

Later that evening they were talking to Aunt Gertrude about Dr. Montrose when the alarm buzzers sounded. The visitors proved to be Biff Hooper and Tony Prito. Both were highly excited.

"What's up?" Joe demanded.

"Plenty!" Tony was panting for breath. "You remember that yarn Clams Dagget told us about seeing lights on Rocky Isle?"

"Sure. What about them?" Frank said. "They've been seen again?"

"Yes. This time by Biff and me. We were out in my Napoli Napoli and spotted those lights and spotted those lights ourselves! They were blinking on and off, as if someone was sending a message in secret code!"

CHAPTER XVII.

The Cliffside Cave.

"Wow!" Joe cried. "Let's get going, fellows! Now's our chance to find out who's sending secret signals from Rocky Isle!"

"We'll have to wait for Chet and Jim," Biff put in. "They'll be right over."

"Okay. We can all go in the Sleuth," Sleuth," Frank said. Frank said.

Chet's noisy jalopy pulled up outside a few moments later. Jim was with him. The other boys rushed out, some sliding into the Hardys' convertible, the others into Chet's "hot rod."

They drove to the town pier.

"Let's make sure the Hai Hau's Hai Hau's all right before we leave," Frank suggested. all right before we leave," Frank suggested.

The boys found that Detective Sm.u.f.f and Patrolman Con Riley had been a.s.signed as police guards for the junk. Seeing the pair, Joe and Frank looked at one another. The two officers were not known as the most astute men on the force.