After a moment, he saw Hawkins peer out from his refuge. Satisfied that he had shaken off his pursuer, the seaman walked calmly along the row of stores and en-iered a grocery shop.
Joe went to the window of the shop and stealthily looked in. Hawkins was at the counter, ordering a supply of groceries.
"I guess that"ll hold him for a while," Joe mused.
He went back to the phone booth in the drugstore nd called Frank.
"Meet me as fast as you can," Joe instructed his 149 brother. He recounted briefly Hawkins" meeting with the man with the limp and described the location of the store from which he was telephoning.
Frank hung up.
"It was Joe," he explained to Mr. Hardy. "He"s trailed Hawkins to a grocery store on the water front. It looks to Joe as though the sailor"s buying a lot of supplies."
"They probably are for Klenger and his gang up on the mountain," Mr. Hardy decided, after Frank had relayed to him Joe"s information.
Frank nodded and slipped into his jacket.
"I wish you"d come to Skull Mountain with us, Dad," he declared. "I bet working together, we could clear up the mystery of Dr. Foster"s disappearance in no time!"
His father smiled.
"I"m expecting an important phone call from Washington," he told Frank. "I"ll join you and Joe as soon as it"s come through."
Frank picked up the basket of food Aunt Gertrude had packed for him while he was waiting for Joe"s call, and went to the door.
"Good-bye, everybody!" he shouted.
Aunt Gertrude"s head poked around the kitchen door, and Mrs. Hardy came running down the stairs.
"Don"t jostle that basket!" his aunt snapped. "There"s a lemon meringue pie on top!"
350 "Take care of yourself, Frank," his mother told him anxiously. "Remember, you"ve just been through a bad experience!"
Frank grinned at her rea.s.suringly and kissed the *sip of her nose.
"I"ll be all right, Mom."
He waved, and ran down the porch steps toward the roadster.
Joe was waiting for him impatiently outside the drugstore.
"Hawkins loaded the supplies in an old jalopy and lit out five minutes ago," he told Frank as he hopped into the seat beside him.
"Never mind," Frank said. "Maybe we"ll catch up with him on the road. I wonder whose car it is."
A few miles out of Bayport on the highway leading toward Skull Mountain the boys saw a dilapidated old sedan ahead of them.
"That"s the car!" Joe exclaimed.
Frank let the roadster slow down and adjusted its speed to the sedan"s rattling pace.
"Think he"ll lead us to Klenger-and maybe Dr. Foster?" Joe asked after a while.
"Hope so," Frank replied. "I doubt if he"s going to eat all those groceries himself. From the look of that crate in the back seat of his car, he"s got enough food to last him for weeks!"
A few miles farther, the sedan turned off onto the dirt road which led directly to the mountain. Frank 151 and Joe followed in the roadster at a discreet distance. At the "toot of the narrow, winding trail which mounted the slope to the ridge, the jalopy Stopped. Quickly Frank drove the roadster behind 3. 3. clump of trees and braked. clump of trees and braked.
A man the boys had never seen came out of the brush and helped Hawkins lift the heavy crate from ihe sedan. Together they started to carry it up the trail.
The boys waited until Hawkins and his companion were well up the path, then followed.
The trip to the top of the mountain took three times as long long as it usually took the boys, for the as it usually took the boys, for the men frequently had to stop to rest.
Finally, Hawkins and the stranger reached the crest of the mountain and disappeared over a rocky ledge. Frank and Joe quickly climbed the last steep section of the trail and peered along the crest of the ridge.
The stocky sailor and his helper had vanished-vanished so completely the earth seemed to have swallowed them up!
CHAPTER XVII.
Mountain Smokestack.
the two boys stared at each other. Then their eyes again traveled over the crest.
There was no sign of the men.
"What in heck happened to them?" Joe said at last.
Frank shook his head. "It beats me," he replied. "I don"t see where they could possibly have disappeared to in the time it took us to follow them over the ledge."
The mountain ridge was covered with trees, rocks and underbrush. But at the top of the trail, where Frank and Joe were standing, the land was comparatively clear.
There were a few blueberry bushes which grew only as high as the boys" knees-much too shallow to conceal even a child.
"Come on," Joe said impatiently. "This is getting us nowhere."
They started down the valley toward the reservoir, and a half hour later they arrived at the camp.
152.
153 The boys had been away from the mountain for a little more than two-and-a-half days, but Bob and d.i.c.k greeted them as if they had been gone for years. It took them a full hour to recount their various adventures since they last had seen the engineers.
"We"re convinced now that Dr. Foster"s disappearance is connected in some way with the water"s escaping from the reservoir," said Joe as he finished his part of the story.
Frank winked at his brother.
"Have you and d.i.c.k any new theories about that, Bob?" he inquired innocently.
Bob"s mouth grew stubborn. "I"m still sticking to my original theory," he said flatly.
"Somewhere in this blankety mountain is a subterranean pa.s.sage which is draining the water into the sea."
"You"re perfectly right," Joe told him solemnly.
"Eh?" Bob stared at him suspiciously.
Frank and Joe couldn"t contain their news any longer.
"You"re right, Bob!" Frank almost shouted. "There is is a tunnel!" a tunnel!"
"We found its outlet in the bay!" Joe cried.
"What-?"
"How-?"
The two engineers looked from one boy to the other. Finally Bob found his voice.
"Suppose we sit down and discuss this calmly," he said, the words almost sticking in his throat.
Frank told him of the articles the boys had planted 154 in the reservoir the night they had left for Bayport, and of finding the decoy and barrel stave two nights later in the bay.
"The water is escaping through the tunnel at night," the boy pointed out. "That"s why your shingles didn"t reveal any escaping currents during the day."
d.i.c.k looked puzzled.
"I don"t get it," he said. "What"s to stop the tunnel from draining off the water in the daytime, too?"
"That"s where Klenger and the others come in," Joe told him. "They must have devised a way to drain off the water only when it suits them."
"And it suits them at night," Frank put in, "because they figure you"ll have a tougher time tracing the current in the dark!"
Bob"s jaw tightened grimly as he saw clearly now that the water shortage was no accident.
He stared at the mountain slopes, and the boys saw his fingers flex and tighten into fists.
Then the tall engineer turned back to them.
"Thanks to you fellows, we now know that the reservoir is not being emptied naturally,"
he said. "We even know some of the people who are interested in keeping the reservoir from filling. We know that the thing is happening at night. So it is up to us to go on the night shift, too. But first, let"s make one more try to see what we can find by day-light."
155 After lunch, the two engineers and the two boys set out to search for their first objective: the entrance to the subterranean channel.
They decided to approach the job systematically -Bob and d.i.c.k to circle the reservoir in the skiff and inspect the sh.o.r.e along the water line, Frank and Joe to accompany them along the sh.o.r.e and investigate the slopes a few feet above the present tvater line.
"You fellows know," said Bob, "that the level of Ihe water rises during the day and lowers at night."
"In other words," d.i.c.k added, "there"s a strip of land eight feet wide running around the reservoir. Every evening it is completely covered with water -and every morning it is completely above water."
"And somewhere in that strip," Bob said, "is the mouth of the tunnel-if we can only locate it."
Hour after hour pa.s.sed as they inspected the strip, prodding and tearing away patches of densely matted vines and shrubs with long poles and sticks and hatchets.
The p.r.i.c.kly foliage clung tenaciously to the rocky slope and painfully scratched the boys"
hands and ankles when they penetrated the underbrush for a closer inspection. But Frank and Joe were determined not to overlook a single suspicious-looking bit of terrain. Any one of these dark-green patches might conceal the mouth of the underground pa.s.sage.
After supper, they resumed their search. As dusk 156 began to settle over the valley, they saw that the water level again was beginning to lower.
The boys turned back toward the camp again. Then, in the clear yellow light which still bathed the top of Skull Mountain, they saw a column of smoke rising from the crest.
They watched it in silence. Then Frank gripped foe"s arm.
"Notice anything different about that smoke?" he usked.
Joe stared at it for a moment, then shook his head.
"Maybe it"s because we"re seeing it from another angle," Frank told him, "but it looks to me as though it"s rising from the clearing where Hawkins and the other guy disappeared so suddenly at the top of the trail!"
"You"re right!" Joe cried. "It is!"
They shouted to Bob and d.i.c.k in the skiff, saying they would join the engineers later, and started up the hillside.
Darkness closed in around them as they climbed steadily toward the still-visible stream of smoke.
"I hope it"s still smoking when we get there," Joe grunted, as he mounted a particularly steep section of the slope. "I"ve run up and down this hill so often I feel like a mountain goat!"
No sooner had he spoken the words than the column of smoke disappeared.
157 Joe picked up a rock and threw it at the ridge.
"That does it!" he declared disgustedly. "From now on the whole mountain can go up in smoke, for all I care!"
Frank smiled in spite of himself. He felt much the same as Joe, but he was determined to find the source of the smoke.
"Come on," he urged. "We"ve almost reached the top. It would be foolish to turn back now."
"Okay."
Joe gave his a.s.sent reluctantly, but secretly he was still as eager as Frank to find the source of this baffling phenomenon.
Clambering over rocks in the now almost complete darkness, they finally arrived at the treeless patch at the top of the trail.