For a moment the man looked surprised, then smiled. "Of course! Ken works here-does odd
jobs for us around the mill. You must be the boys he met yesterday when he was delivering
some copy to the printer."
"Yes," Frank replied. "When we asked Ken about his job he was very secretive."
"Well," the maintenance man said, "he has to be! This plant is doing top-secret work. All of us have been impressed with the necessity of not talking about Elekton at all."
"Is Ken around?" Joe asked nonchalantly. "We'd like to say hello."
"I'm afraid not," was the reply. "We sent him by bus this afternoon to do an errand. He won't be back until later." The man excused himself and resumed his clipping.
"We'd better eat." Iola giggled. "My poor brother is suffering."
"I sure am!" Chet rolled his eyes. Laughing, the picnickers started away.
Joe, who was in the rear, happened to glance up at the front of the mill. He was startled to
catch a glimpse of a face at one of the second-story windows. He stopped in his tracks.
"Ken Blake I" Joe said to himself.
As the young sleuth stared, mystified, the face disappeared from the window.
CHAPTER VI
A Mysterious Tunnel
PUZZLED, Joe continued looking up at the window of the old mill.
"What's the matter?" Iola asked him. "Did you see a ghost?"
In a low whisper Joe explained about the face which had disappeared. "I'm sure it was Ken Blake I saw at that window!"
The others followed his gaze. "No one's there now," Iola said. "Of course the glass in all the windows is old and wavy. The sunlight on them could cause an illusion."
Chet agreed. "How could Ken be here if he was sent on an errand?"
Joe stood for a minute, deep in thought. "I can't figure it out, but I'm sure that it was no illusion.
Come on, Frank. Let's go check."
While the others walked down the hill, the Hardys strode up to the maintenance man, who was
still trimming hedges.
"Are you sure Ken went into town?" Joe asked. "Just now I thought I saw him looking out a second-floor window."
"You couldn't have. You must have been dreaming." The man gave a jovial laugh.
Joe was still not convinced. Impulsively he asked, "Does Ken ever run any errands for you at night?"
"No," the man answered readily. "He leaves his bike here and walks home when we close at five-thirty."
"Does anyone else have access to the bike after that?" Frank queried.
"It's kept in an open storage area under the rear of the mill and could be taken from there easily."
Although obviously curious, the man did not ask the Hardys the reason for their questions. He
looked at his watch.
"Excuse me, boys, I'm late for lunch." He turned and hurried into the mill.
As the brothers hastened to catch up with Chet and the girls, Frank said, "Another thing which makes me wonder if that bicycle is connected with the warning is the description of the boy
who bought the pedal.
He could be Ken Blake."
"I agree," Joe said. "I'd sure like to question Ken."
"We'll come back another time," Frank proposed.
The group picked up the picnic hamper from the Queen and strolled down a narrow path,
through the woods leading to Willow River.
"Here's a good spot." Callie pointed to a shaded level area along the bank. "We haven't been in this section before."
Soon everyone was enjoying the delicious lunch the girls had prepared: chicken sandwiches,
potato salad, chocolate cake, and lemonade. While they were eating, the girls were the targets of good-natured kidding.
"Boy!" Joe exclaimed as he finished his piece of cake. "This is almost as good as my mother and Aunt Gertrude make."
"That's a compliment!" Chet said emphatically.
Callie's eyes twinkled. "I know it is. Joe's mother and aunt are the best cooks ever!"
Iola sniffed. "I don't know about this compliment stuff. There's something on your mind, Joe Hardy!"
Joe grinned. "How are you on apple pie and cream puffs and-?"
"Oh, stop it!" Iola commanded. "Otherwise, you won't get a second piece of cake!"
"I give up." Joe handed over his paper plate.
After lunch everyone but Chet was ready to relax in the sun. Normally he was the first one to
suggest a period of rest, even a nap, but now his new project was uppermost in his mind.
"Let's start to collect the specimens for my microscope," he urged his friends.
The Hardys groaned good-naturedly at Chet's enthusiasm, but readily agreed.
"We'll need some exercise to work off that meal." Frank grinned.
The girls packed the food wrappings in the hamper. Then, single file, the group walked
downstream, paying careful attention to the rocks and vegetation. Chet picked up several rocks and leaves, but discarded them as being too common.
"Are you looking for something from the Stone Age?" Joe quipped. "Maybe a prehistoric fossil?"
"Wouldn't you be surprised if I found one?" Chet retorted.
They followed a bend in the river and came to a small cove with a rocky, shelving beach. Here
the willow trees did not grow so thickly. The shoreline curved gently around to the right before it came to a halt in a sandy strip along the riverbank.
"What a nice spot," said Callie. "We'll have to come here again and wear our swim suits."
"Look!" cried Iola. "What's that?"
She pointed to a dark opening beneath a rocky ledge which bordered the beach.
"A cave!" exclaimed Joe and Frank together.
Intrigued, the five hurried along the beach for a closer look. Eagerly the Hardys and Chet
peered inside the entrance. The interior was damp, and the cave's walls were covered with
green growth.
"This'll be a perfect spot to look for specimens," Chet said. "Let's go in!"
The boys entered the cave. The girls, however, decided to stay outside.
"Too spooky-and crowded!" Callie declared. "Iola and I will sun ourselves while you boys explore."
The Hardys and Chet could just about stand up in the low-ceilinged cave. Frank turned on his
pocket flashlight and pointed to an unusual yellow-green fungus on the right side of the cave.
"Here's a good sample of lichens, Chet."
Soon the boys were busy scraping various lichens off the rocks. Gradually they moved deeper
into the cave. Frank halted in front of a pile of rocks at the rear.
"There ought to be some interesting specimens behind these stones," he said. "They look loose enough to
move."
Together, the three boys rolled some of the rocks to one side. To their great surprise, the
stones had concealed another dark hole.
"Hey! This looks like a tunnel!"
Excitedly Joe poked his flashlight into the opening. In its beam they could see that the hole
appeared to extend into the side of the bank.
"Let's see where the tunnel goes!" Joe urged.
"Okay," Frank agreed eagerly. "We'll have to move more of these rocks before we can climb through. I wonder who put them here and why."
Rapidly the boys pushed rocks aside until the narrow tunnel entrance was completely exposed.
Joe crawled in first, then Frank.
Chet tried to squeeze his bulky form through the space but quickly backed out. "It's too tight for me," he groaned. "I'll stay here and collect more specimens. Anyhow, I'll bet some animal made the tunnel and it doesn't lead anywhere."
"I'm sure no animal did this," Joe called back, aiming his flashlight at the earthen walls of the tunnel. "Look how hard-packed the sides are-as if dug out by a shovel,"
Frank was of the same opinion. He pointed to rough-hewn wooden stakes placed at intervals