Frank hauled in the oars, and Joe dropped the duck in the water.

Frank rowed on, keeping the skiff a few feet from "che sh.o.r.e. Then Joe and Chet dropped overboard the painted yellow-pine board, and finally the barrel stave.

It was late when they finished circling the reservoir, but they had the satisfaction of knowing that if the underground channel existed, at least one of their articles was bound to be sucked into it.

"How long do you suppose it will take for tliu tliu junk to go through the tunnel?" asked Joe. junk to go through the tunnel?" asked Joe.

Frank thought for a moment, then he said, "G1 course, we don't know for sure where the stream comes out. The geological guy in the book Bob Carpenter read thought the stream flowed into the bay down near Bayport."

"That's twenty miles-"

Frank interrupted. "-as the crow flies. But how 84 do we know the underground channel takes the most direct way? And how do we know there aren't ledges and rocks and obstructions on which the things we've dumped in here will get caught?"

"Besides," said Joe, "we have to remember that the water is actually flowing through the old stream bed only a few hours at night."

"That's right," agreed Frank. "If this thing were a straight flume or chute like a millrace, the things we planted could get to the bay, if that's where it ends, in a couple of hours. But my guess would be that it will be more like a couple of days."

Joe nodded. "All the same, we had better plan to make a search for the stuff as soon as we can. The tide could carry it out of the bay, and then we'd never know."

Frank hooked the skiff to its mooring line and stepped ash.o.r.e.

"Well, that's that," he said, looking out over the water. "What say we drive back to Bayport?"

"Suits me," Joe replied.

"Me, too," Chet chimed in. He glanced at his watch. "I wonder if Aunt Gertrude will feel like a midnight snack?" he asked innocently.

Joe grinned. "She will if you ask her!"

Chet started toward the tents. "Then let's get going!" he called over his shoulder. "We haven'C much time!"

85 They packed a few things they would need, and Frank wrote a note to Bob and d.i.c.k telling them about the hermit and saying the boys would return in a day or two. He propped up the note on Bob's cot, where the engineer would be sure to see it.

Aunt Gertrude was in bed reading when the Hardy boys drove up to the house in their roadster. But when she heard how Chet had set his heart on having a slice of her pie or cake before going home, she good-naturedly put on a robe and came right down.

Soon, Frank and Joe, as well as Chet, were wolfing sandwiches, gulping milk and attacking generous slices of cherry pie.

Aunt Gertrude looked at them with astonishment.

"What in the world have you been doing up there in the mountain?" she demanded. "You act as if you haven't eaten for a week!"

Frank told her a few of the things that had happened to them, and his aunt clucked disapprovingly. Although she tried not to show it, the maiden lady worried constantly about the boys' activities, and it was always a relief to her when they were safe at home.

"Where's Dad?" Joe asked finally.

"He had a telephone call this evening and went out," Aunt Gertrude said. "He said he wouldn't be back until tomorrow."

86 "Was the call about the Foster case?" Frank questioned her eagerly.

"I don't know," she replied tartly. "You ought to know by now that your father doesn't confide in me about his work."

Chet ate the last crumb of his pie and looked wistfully at his empty plate. Then he stood up with a sigh.

"I gotta be going," he announced to the boys. "See you tomorrow." He beamed at Aunt Gertrude. "Thanks for the pie."

The next day the boys were at breakfast when the telephone rang.

Mrs. Hardy answered the call.

"It's Gallic," she told Frank. "She says she must see you right away!"

"Where is she?" Frank asked, pushing back his chair.

"She's in a drugstore a few doors from Mr. Klen-ger's plumbing shop," his mother went on. "She says she has some important news for you!"

"I better get right over!" Frank said excitedly, thrusting his arms into the sleeves of his jacket.

"I'll go with you!" Joe put in promptly.

"Okay-but hurry!" Frank called, rushing out the door. "I'll get the car!"

Frank found ar empty parking s.p.a.ce in front of the drugstore and expertly jockeyed the roadster into it. Gallic ran to meet them as the boys got out.

87 "What happened?" Frank asked worriedly. "You look frightened!"

"I am," Gallic said. "At least, I was," she amended with a little laugh. "I'm getting over it, now."

She looked nervously up and down the street, then beckoned the two boys into the doorway of a vacant store where they could not easily be seen.

"Mr. Klenger fired me this morning," Gallic said, as soon as they were off the sidewalk.

Frank's eyes widened. "What for?" he asked.

"He caught me copying down a telegram he'd received," Gallic explained. "He was furious. I never saw a man so mad in my life!"

"What did the telegram say?" Joe queried her eagerly.

"Mr. Klenger tore up the copy I was making," Gallic told him, "but I remember the words." She wrinkled her brow in thought as Frank and Joe waited on tenterhooks for the message. "It went like this," Gallic said.

"Wait," Frank said hurriedly. "I'll write them down."

He took a small notebook and a pencil from his pocket.

"Okay, shoot!"

"The message said: 'Syndicate convinced you are stalling. What's wrong? Can Retsof deliver? When?' And it was signed 'Ben.' "

88 Frank scribbled the last words of the message, and the two Hardy boys studied them with puzzled frowns.

"Retsof," Frank mused. "Sounds like a Russian name."

"Maybe it's a code name," Joe suggested.

"Could be," Frank agreed, studying the word thoughtfully. "I've got it!" he cried suddenly.

"It's Foster spelled backward!"

Joe's eyes glistened.

"That's definite proof Klenger is mixed up in Dr. Foster's disappearance!" he crowed.

The boys grinned at one another with rising excitement.

"Where did the message come from, Gallic?" Frank questioned the pretty brown-haired girl.

"Chicago," she answered promptly. "It arrived this morning."

"What did Klenger say when he caught you copying it?"

"He called me a snooper, Frank! He said he just wouldn't have nosey people around.

He said I was through."

"When did all this happen?" asked Frank.

"It happened just after a man came to see Mr. Klenger," Gallic went on.

"A tall, thin man?" Frank asked quickly.

"Yes," Gallic said, surprised. "Mr. Klenger called him 'Sweeper.' "

"I thought so," Frank remarked grimly. "Sweeper is the man we saw on the mountain, talking to Sailor Hawkins," he told Joe, "and one of the men who held me up," he added.

Frank thought for a moment. "Maybe we'd better have a talk with Klenger," he decided finally.

"You can't!" Gallic cried. "He closed his shop right after he fired me. He said he was leaving town!"

The boys stared at her with dismay. If Klenger left Bayport, they might never locate the key to the two mysteries!

They drove Gallic home. There Frank asked for the telephone directory.

"I'm going to look up Klenger's address," he told Joe. "If he told Gallic the truth, maybe he's still home packing."

Frank wrote down Klenger's street and number, and a moment later he swung the roadster in the direction of the house.

It was a frame house, set back from the street by a short lawn. As the boys went up the steps to the porch, they saw that the window shades were drawn.

Frank rang the doorbell, but there was no answer. Joe tried to peer through a window, but the shade completely shut off his view.

They returned to the car, and as he got in Joe iiooked over his shoulder. Was it his imagination-*

90 or for a moment had he actually seen a woman's face staring at the boys from an upstairs window?

He told Frank about the face, and his brother deliberated.

"If it was Klenger's wife," he said thoughtfully, "he can't have gone away for good. We'll go back some other time and try our luck."

Mr. Hardy had returned when the boys arrived home. They showed him Frank's copy of the telegram Klenger had received, and he studied it with great care.

"There's no doubt now that Klenger is a man we've got to watch," the detective said.

Frank told him of the possibility that Klenger had left Bayport, and his father frowned.

"I'll check on that."

Mr. Hardy reached for the phone.

"Get me long-distance-Chicago," he told the operator. He glanced at the telegram on his desk. "I'm going to try to trace the sender of this message," he explained to the boys.

Frank and Joe left their father to complete his call.

"You know something?" asked Frank when they were outside the study door. "The sooner we take the Sleuth Sleuth and begin to look for the articles we dropped into the reservoir and begin to look for the articles we dropped into the reservoir last evening the better. The tide will be going out in another hour."

"Let's go," Joe replied.

91 They drove to the boathouse where they kept their speedboat. Frank stepped into the c.o.c.kpit of the trim little craft and pushed the starter b.u.t.ton.

The motor failed to catch at first, and Frank put out his hand to try again. But before he made contact, the boys heard the roar of a motorcycle as it came to a stop behind the boathouse.

The machine's motor misfired, then sputtered loudly with a peculiar, uneven rhythm. A moment later, it stopped.

Joe saw a tense look come over his brother's face.

"What is it, Frank?" he asked quickly.

"That motorcycle!" Frank whispered. "It sounds like the machine Sweeper was riding the night he held me up!"

CHAPTER XI.

A Visit to Brookside.

frank leaped from the Sleuth Sleuth and ran toward the rear of the boathouse. Joe followed, and ran toward the rear of the boathouse. Joe followed, close on his brother's heels.