At that moment Karl Driscoll walked into the room. He stared at the girls, then nodded curtly, looking annoyed at their presence. Nancy wondered if they had disturbed some project of his. As if lost in thought, she walked toward the window. Suddenly Nancy asked, "Who is that red-haired girl down on the beach? Do you know her?"

The question had an electrifying effect on the Driscolls. They rushed to the window and looked out over the bluff. Cecily was in plain sight below. Now she turned as if heading for the misty end of the lake. With a muttered excuse, Karl Driscoll fairly ran into the kitchen. The girls dared not follow, but they heard a door close softly and footsteps pounding down the cellar stairs.

Nancy continued to look out the window and in about two minutes she spotted two men on the beach-Karl Driscoll and his brother Vince! How had they reached it without her seeing them leave the house? "I'm sure now they use an underground passage," Nancy thought. The men started off on a run toward the misty end of the lake and disappeared around a bend. Cecily could no longer be seen.

With difficulty, Nancy kept calm. She was sure her ruse had worked! The other red-haired girl was being held in the house and the Driscolls thought she had escaped!

"Now to hunt for the prisoner!" Nancy thought.

CHAPTER XVII.

The Mysterious Beach House

As Nancy wondered how she could get upstairs to investigate the room with the bulls'-eye window, she saw Mrs. Driscoll looking hard at her, Bess, and George.

"I think you've done enough searching," the woman said crisply. "You'd all better go now."

Nancy knew she could not force the issue. Disappointed, she and her friends thanked Mrs. Driscoll and went outside.

"I hope those two men didn't catch up with Cecily," Bess said worriedly.

George chuckled. "She had a good head start. I'm sure she doubled back and is safely locked in the cottage."

The girls lingered nearby, hidden among the trees. This was the spot where they were to meet the three boys, who came along a few minutes later.

"Any luck?" Nancy asked them.

Ned replied, "No one came out of the house."

Nancy explained what had happened and the boys gave low whistles. "Wow!" said Burt. "The Driscoll brothers really took the bait!"

"Yes," said Nancy. "But I wish we could have gone upstairs."

Suddenly Bess warned, "Ssh! Here come Mrs. Driscoll and the twins."

The six kept motionless in their hiding place. The woman did not seem to be searching for anyone, however. Yanking a child by each hand, she hurried down the bluff path and set off along the beach in the direction her husband and brother-in-law had taken.

"Now's our chance!" Nancy said. "If the girl is a prisoner in that house, we must set her free!"

She and the others hurried to the door. It was locked, as was the one to the kitchen.

Nancy turned to Ned and pointed out the bull's-eye window, which was open. "Do you think you can toss a stone through that window?"

Ned was sure he could. As the group moved through the woods toward the far side of the house, he began looking for a suitable stone.

Nancy rummaged through her handbag for a piece of paper on which to write a message. She did not find any, and the others confessed that they had neither paper nor pencil.

"It doesn't matter," said Nancy. "If the girl is locked in that room, she'll know the stone wasn't thrown by her enemies-there would be no reason for them to do so. I'm hoping she'll realize someone is trying to help her."

Ned stood far enough back, took careful aim, and threw the stone as if it were a high forward pass. It sailed neatly through the round opening! The group below waited tensely for a response. A few minutes went by in complete silence, and they began to despair. Maybe no one was in the room. Then suddenly the stone was tossed out the window!

Nancy was excited. "Someone is a prisoner in there!"

Burt spoke up. "I can't understand why the Driscolls didn't check the attic room before they rushed after Cecily."

Nancy replied, "My guess is that Karl was so excited at seeing the red-haired girl nothing else entered his mind except that his prisoner had escaped. He rushed down to the cellar, found Vince, and dashed to the beach through a secret tunnel. But, in the meantime, Mrs. Driscoll probably was suspicious, and went to the attic to find out. When she discovered the other red-haired girl still there, she grabbed the twins, and went to warn the men-"

She stopped speaking abruptly at the sound of voices in the woods below. In a short while the hidden group could see the three Driscoll adults and the twins coming back to the house. As they came nearer, the little boy cried out, "I wanted to play in the water!"

"Shut up, you brat!" Karl Driscoll said, slapping the boy hard.

The little girl began crying as she tried to comfort her brother. Mrs. Driscoll hustled them into the house and the men followed.

Nancy again thought of her secret hunch. 'It's doubly important for us to get to Susan Wayne-or whoever the red-haired girl is-to learn if I'm right," she said to herself.

"I'd like to sock that guy!" Ned burst out, and the others nodded vigorously.

Then Nancy suggested that Bess, George, Burt, and Dave station themselves to watch the house from every angle. "Ned and I will first check on Cecily. Next, we'll drive to town and tell our story to Chief Stovall. I hope hell come and make an investigation."

The couple hurried off to get Ned's car. They found Cecily in the cottage, cautioned her to keep the door locked, and assured her they would tell her everything later. The trip to Misty Lake village did not take long. Chief Stovall was on duty. He listened patiently to Nancy's account, but was obviously skeptical. "Your evidence is pretty flimsy, Miss Drew," he said.

The young sleuth reddened but did not reply. Her blue eyes held a disapproving look, however, and finally the chief promised that he himself would come out with one of his men and look over the lodge premises.

"Please! Can't you come now?" she urged.

The chief smiled. "You are an impatient young lady. Well, I guess we can make it."

When the two cars reached the right-hand fork which led to Pudding Stone Lodge, Nancy suggested that the chief wait until she checked with her friends to find out what had happened at the lodge. But the watchers had nothing to report.

"No one has left the house," George announced.

"That's fine," said Nancy. "The police are ready to go in."

She and Ned ran back to the squad car and gave this news to the officers. "When we see you come out, we'll meet you here," Nancy said.

The six friends stationed themselves in an evergreen grove and peered out. They saw Karl Driscoll open the door and readily admit the police. Nancy thought she detected a momentary look of fright on his face. Time dragged by. Finally the two officers came out. To Nancy's consternation, thay parted from the Driscolls on what seemed to be very pleasant terms.

Puzzled, the whole group made their way through the woods to the spot where the police car was waiting. Chief Stovall leaned out the window and addressed himself to Nancy.

"We didn't find a thing. We even broke into that locked attic room to be sure. No sign of any prisoner. Besides, those people don't seem in the least suspicious. Miss Drew, I feel that you may have overstepped in this situation. You know trespassing is against the law. I warn you to stay away from the lodge. You've caused the Driscolls enough inconvenience."

Nancy was too embarrassed and crushed even to argue. Chief Stovall said that he and his man had searched every corner of the house from attic to cellar. "So I'm sure you all can spend the rest of your vacation here just having fun."

Despite the jolt to her spirits, Nancy politely thanked the chief for his time and effort, then the group said good-by. They were silent on the walk back to the cottage. Nancy's friends felt sorry for her-she had worked so hard to solve the mystery and now everything she had achieved seemed to be crashing into bits.