"Oh, you be, be you!" Annie cut him short. "Then you git on back there, if you know whut's good fer you! Ain't no engineers goin' to traipse on my land!"

"We're not engineers," Joe tried to explain. -We're-"

But Potato Annie was deaf to any voice but her own. "You hear me! Git!

Good-fer-nothin' loafers-drivin* self-respectin' people off their prop-pity!"

Annie bent double and rocked with sudden pain. She looked up at the boys, her eyes reflecting her misery, and whispered, "If I didn't have the rheu-matiz, I'd run you off myself!"

Frank went to her quickly and held her arm. "Let me help you," he begged.

Annie peered at him suspiciously. Then she said grudgingly, "They's some pills in the house-on the table. If I could have one o' them, it would relieve me some."

"I'll get the pills!" Joe told her.

24 He ran into the house and returned a moment later with a small green bottle. Potato Annie unscrewed the lid, swallowed a pill with a grimace, screwed the lid on again and put the bottle in the pocket of her ap.r.o.n.

She studied the boys carefully. "Whut you want?" she said at last.

"We came for some information," Frank told her.

He described the column of smoke he had seen, and the explosion, but although Annie admitted having seen the smoke and having heard the explo* eions, she claimed she knew nothing about them.

"Have you ever come across any skulls around here?" Joe put in.

"Skulls?" scoffed the old woman. "Why, they's a million of 'em buried on the other side o'

this mountain! And they's plenty o' skulls scattered on this side, too! My grandpaw told me the whole Injun tribe died o' cholery. No water from this mountain'll ever be fit to drink!" She cackled with sudden mirth. "Tell that that to your engineer friends!" to your engineer friends!"

Frank tried another tack. "Do you know an old man who lives on the mountain?" he asked. "A gaunt-faced man, with long, s.h.a.ggy hair-?"

Annie's head jerked up suddenly, and into her eyes crept an undeniable look of fright!

CHAPTER IV.

Chet Joins Up.

in the next instant the old woman's eyes went blank, and she declared flatly that she had never seen nor heard of such a creature.

Frank thanked Annie for her information, and the old woman sniffed.

"Ain't told you nuthin', fur as I know." She watched the boys start down the slope in the direction from which they had come. "Tell them engineers this valley ain't never goin' to be covered with water!" she yelled after them. "Tell 'em Annie said so!"

The boys grinned at one another and looked back. Annie was bending over her potato plants again.

When they reached the camp, they saw Bob and d.i.c.k slowly circling the partly filled reservoir in a rowboat. d.i.c.k swung the oars, while at regular intervals Bob dropped white-painted shingles into the water.

Frank waved, and d.i.c.k pulled the boat toward them. He rested his oars a few yards from the sh.o.r.e, and the boat swung easily alongside the boys.

"What are you doing?" Joe asked.

"Trying to find out where the water is escaping," Bob explained. "The river is feeding the reservoir okay, but the water won't rise over twenty feet. Somewhere, somehow-it's draining out."

"The shingles will help us to detect currents where the water may be escaping," d.i.c.k added,, "What have you two been up to?"

Frank described how the trail of the footprints had led them to Potato Annie. "I guess we didn't accomplish much," he said dispiritedly.

"Buck up!" Bob said rea.s.suringly. "You fellows can't expect to solve this thing the first day."

Frank smiled and reminded Joe that they had promised their mother to return home that day.

"We'll be back before nightfall," he told the two engineers.

"You bet," Joe put in. "Wild horses couldn't keep us away from this mountain after what's happened!"

Bob waved, and d.i.c.k swung the boa': away from the sh.o.r.e. Some time later, as the boys stood on the ridge before descending the trail to their car, they saw the boat still circling the reservoir-looking, from where they were, like a tiny chip of wood.

An hour later when the Hardy boys drove up to 27 their home, Aunt Gertrude was on the lawn, digging out dandelions. Joe, his eyes twinkling, picked up the skull from the seat beside him and held it in front of him as he got out of the car.

"Hi, Aunt Gertrude," he greeted. "We'd like to have you meet a friend of ours!"

The tall, graying woman gave a shriek and almost lost her balance trying to get away from her nephew. Joe slowly but relentlessly pursued her.

"Get away from me, Joe Hardy!" Aunt Gertrude cried. "Get away, I say!"

Joe laughed. "Okay, Auntie," he said impishly. "But that's no way to win friends!"

He started up the path toward the door, and Frank joined him.

"Don't you dare take that horrible thing into the house!" Aunt Gertrude cried after them.

"If you must keep it, put it in your workshop where decent people won't have to look at it!"

The boys grinned and went to the room over the garage which they used as a combination workshop and clubhouse for their friends.

A few years before, the third floor of the Hardy house had been theirs to do with as they pleased. But as their sleuthing interests widened to include fingerprinting and chemical a.n.a.lysis, Aunt Gertrude had declared they might blow up the house, and had insisted that her nephews transfer their activities to the room over the garage.

28 From the time Frank and Joe had solved their first mystery, that of the "Tower Treasure," down to their most recent case, they had always found Aunt Gertrude a little hard to cope with.

Their friend, Chet Morton, had also had some lively encounters with Aunt Gertrude. Chet had played an amusing role in the mystery of "The Phantom Freighter," when he took a course in fly-tying and became involved with the Hardy boys in the capture of an elusive band of criminals.

After a quick shower and a change of clothes, the boys went to greet their mother. Mrs.

Hardy made no attempt to conceal her relief at their safe return, but she accepted calmly their announcement that they planned to go back to Skull Mountain that evening.

"I'll prepare an early dinner," she promised them, "so you won't run the risk of traveling over that mountain trail in the dark. It sounds dangerous."

"And /'// bake a cake," Aunt Gertrude told them. "You can take it with you when you go.

Mr. Carpenter must be starved for some decent food. I imagine the poor lamb has been living on herbs and roots and-and nuts all this time."

Joe grinned as his aunt went toward the kitchen. "Put some icing on it, Auntie," he called after her. "A skull and crossbones would be just the thing!"

His aunt glared at him, then disappeared with a swish of her skirt.

29 Late that afternoon, the boys, their mother and aunt sat down to an appetizing dinner of roast beef and vegetables. The talk soon turned to Fen ton Hardy, who had been away from home for the past two weeks.

"What kind of case is he working on?" Frank asked.

"I don't know," Mrs. Hardy confessed. "You know your father. He likes to keep the details of his work to himself." She smiled at the boys. "I suppose he feels I'll have less to worry about that way."

"Fenton's right," Aunt Gertrude said flatly. "Besides, a private detective's business should be private -just like a doctor's, or a lawyer's. That's why he's called a 'private eye'!" be private -just like a doctor's, or a lawyer's. That's why he's called a 'private eye'!"

she finished complacently.

"Why, Aunt Gertrude," Frank said with mock astonishment, "you've been reading detective stories!"

The elderly woman fixed him with a sharp stare. "And why not?" she demanded.

The boys laughed and went on eating. But both could not help wondering what sort of mystery was keeping their father away for so long.

The boys had just downed a double portion of meat and vegetables when they heard a rattletrap car chug into the driveway. A moment later, Chet Morton came into the dining room, greeted the Hardys cordially and drew a chair up to the table 30 without further ceremony. He spread a napkin carefully in his lap, took an extra plate, picked up knife and fork and beamed at them.

The Hardys were accustomed to Chet's behavior. It was a well-established fact that Chet's visits usually coincided with the Hardy family's meal hours. The Mortons lived on a farm and ate all their meals at least an hour earlier than the Hardys. Chet's capacity for good food seemed unlimited.

Chet was always welcome to eat whatever the Hardys had. But now, because dinner had been started earlier and their mountain experiences had made Frank and Joe unusually hungry, there wasn't a sc.r.a.p of food left.

"You're too late, Chet," Frank told him. "We've just finished dinner."

Chet groaned. He looked at his watch. "Gosh," he said plaintively, "I came as quick as I could!"

Joe could not help laughing at the woebegone expression on Chet's face. Next time, he promised, as Aunt Gertrude went into the kitchen, the Hardys would reserve a special plate for Chet.

Aunt Gertrude returned bearing a seven-layer chocolate nut cake. Chet's face lit up as he saw it-but his happiness was short-lived.

"Here's the cake for the camp," Aunt Gertrude told her nephews.

Chet's face quivered slightly as he watched her pack the cake neatly in a box.

21 "Camp? What camp?" he quavered.

Joe winked at Frank. Chet's eyes were fixed hungrily on the cake, and from time to time he wet his lips.

"Bob Carpenter's camp on Skull Mountain," Joe informed young Morton. "Frank and I are working with Bob on the water-shortage mystery."

Chet's interest quickened, but he could not take his eyes from the cake.

"I read about the water shortage," he said. "But what are you fellows doing up there?"

Frank told him of their experiences but carefully omitted any reference to the skull, and his eyes pleaded with Mrs. Hardy and Aunt Gertrude not to give away the adventure.

Joe, sensing Frank's plan, concealed a smile.

"Why don't you come with us to the camp, Chet?" he said casually. "You can help us eat the cake."

Chet beamed at the suggestion, then he eyed Frank and Joe suspiciously.

"I don't know," he said dubiously. "Every time I get mixed up with you two, something happens to make me regret it."

"Nonsense, Chet," Frank said. "What can happen to you on a camping trip?"

"Plenty of things-with you two around," Chet retorted.

He described darkly the dangers of snakes, insects, forest fires, floods, landslides and wild animals.

32 "Well, if you don't want to go-" Frank said finally. He looked at his brother. "Guess we'd better get started, Joe."

Joe nodded and picked up the cake box. He pried the lid slightly open for another look and smacked his lips appreciatively.

This was more than Chet could bear.

"Wait, fellows!" he begged. "I'll go with you!"

Chet accompanied the boys to their workshop to help them carry some camping equipment to the car. When they reached the door, Frank went ahead and pretended to fumble with the light switch.

"Guess the bulb's burned out," he said, as the room remained in darkness.

Joe, who was behind Chet, took a flashlight from his pocket and thrust it into Chet's hand.

"Here, Chet, use this."

Chet beamed the flash into the room-then gave a gasp. The flashlight clattered on the floor.

"What's the matter?" Frank asked.

"Th-there's a skull in there!" Chet cried. "It looked right at me!" He struggled to pa.s.s Joe. "Let me out of here!"

"You must be seeing things!" Frank laughed. "I'll show you."

He trained the flashlight on the skull.

"There it is again!" Chet yelled.