She tugged and pushed, but the door would not budge. Had it locked automatically-or had the door been bolted from the inside by one of the Driscolls? And if so, what was the reason? The only explanation she could think of was that these mysterious people wanted to keep her out of the house until they had accomplished something about which they did not want her to know.

Nancy looked off into the distance, wondering if she could possibly signal Bess. But at that same moment she saw her friend come from the cottage, lock it, and then hurry up the path to where the car was parked. The faint sound of a motor came to Nancy's ears and she knew Bess had set off for the village.

Nancy tried the door once more with no luck. She began to pound on it loudly. She rapped until her knuckles were sore, but no one came to let her in. Maybe everybody had left the house, she thought.

Exasperated, Nancy began to cry out, "Help! Help! I'm locked out on the roof!"

She kept repeating her plea, but if anyone heard it, he had no intention of coming to her aid.

"I wonder if there's any way to get to the ground from here except through that door." Nancy walked toward the lake side of the house. She leaned over the railing and thought she saw what might be a fire escape. Here the roof sloped sharply. A drainpipe led down it to the gutter.

Nancy decided to lie flat on the roof and edge herself along, holding onto the pipe. If she were right about the fire escape, she could reach it from this angle. Her heart thumping, the young sleuth climbed over the railing and tested the drainpipe. It seemed to be firm.

Nancy let herself down the roof gingerly, and indeed found what was once a fire escape. But time and weather had loosened it from the wall. She knew it would be too hazardous to try climbing down. Besides, there was a ten-foot drop from the end of it to the ground. There was nothing to do but go back to the attic door. "I guess I'll have to break it down!" Nancy thought wryly.

When she reached the door, she blinked unbelievingly. It was open a crack!

"I didn't just dream it was locked," Nancy told herself. "Someone was playing a grim joke on me!"

She hurried down the attic stairs. As she started along the hall Nancy heard quarreling adult voices coming from one of the rooms near that of the twins'.

The next instant the door opened with a bang and Vince Driscoll stepped out. Seeing Nancy, the burly man seized the girl's arm roughly. His face was red with rage and fire seemed to leap from his eyes.

"What are you doing here?" he demanded.

CHAPTER IX.

The Vandal

INDIGNANT, Nancy shook herself loose from Vince Driscoll's grasp. At that moment his sister-in-law came from the same room and glared at him. "Karl and I gave Miss Drew and her friends permission to come here and hunt for an iron bird," she said coldly.

"Why didn't you tell me?" Vince asked sullenly. "I'd have warned you not to. She's snoopy and a troublemaker." He turned to Nancy. "Don't show up here again!"

Mrs. Driscoll set her jaw firmly. "That's for Karl to decide, not you."

Vince seemed about to retort, but instead kept still and stalked on down the hall. Nancy then told Mrs. Driscoll about having been locked out. The woman said, "Vince didn't know you were here and went up to the attic. That door to the roof is not supposed to be open so he locked it. After a while I went up to see why you'd been there so long and found out what had happened. Since you weren't on the balcony I assumed you were somewhere on the roof, and unlocked the door."

"I appreciate that," said Nancy. "I could just picture myself staying out there all night!" She decided to make light of the matter and pretend that she accepted the explanation without question. But she was very suspicious.

Suddenly she thought of the closed-up room with the bull's-eye window. Had the Driscolls locked her out deliberately because they themselves had been keeping something-or someone-hidden in it? "And maybe moved out the person or object while I was outside," Nancy concluded. "It could even have been the red-haired girl. But what's the reason?"

Mrs. Driscoll escorted Nancy to the front door and said good-by pleasantly. "It's too bad the bird in the storage room isn't the one you're looking for," she said. "If we happen to come across another, we'll let you know."

"Thank you," Nancy said, and started down the road. The Driscoll family puzzled her. She wondered about the brothers' maintenance business. "They seem to be home a lot," Nancy thought. "Well, maybe they don't get many calls."

In any case, they certainly did not seem to get along well together!

"Could it be because of the twins?" Nancy reflected. "But why?"

She vividly recalled the hard look Karl Driscoll had given her in the general store. She was sure he was not pleased that the girls were living at the lake. "Though why did he go out of his way to be helpful?"

When Nancy reached the cottage the three girls came out to meet her and she reported her adventure.

Bess was concerned. "Why, Nancy, you might have slipped off that roof and been killed!"

Nancy grinned. "I guess I'm just a tough old sleuth," she answered.

"It's a good thing, because you're in for a surprise," George stated. "Wait until you see this cottage!"

As Nancy walked inside, she stared aghast at the scene before her. Tables and chairs had been broken. Every drawer in the place had been emptied of its contents, which were scattered around the floor. Bess had endeavored to put some of the things away before picking up the other two girls. The three had just started working again when Nancy arrived.

"It's vandalism!" Cecily said to Nancy. "Oh, who would want to do such a thing?"

"So far," said Bess, "we haven't found anything missing."

George nodded. "Some intruders are like that. They get so angry if they can't find what they're looking for, they'll tear a place to pieces."

The girls went on straightening up and repairing the furniture as best they could. As they worked, George and Cecily reported that they had gone to Neal Raskin's office, but he was not there. No one seemed to know where he had gone or when he would return.

Suddenly Bess said, "I'm starved ! Do you real ize it's seven o'clock? I never did start supper, what with this mess!"

The girls stopped working and by seven-thirty were seated around the little table, eating hungrily and chatting over the day's adventures.

"They all seem to add up to nothing," said Cecily, a sad expression in her eyes.

To cheer her, Nancy suggested taking a ride in the canoe. Cecily eagerly accepted.

"You two go," said George. "Bess and I will do the dishes."

Nancy and Cecily each took a paddle, and without even consulting each other, they found themselves heading for Pudding Stone Lodge.

By this time it was late dusk and a mist had begun to rise up from the water. In the foggy area it was thicker than ever.

"We'd better stay away from there," said Cecily. "We might get lost."

Pudding Stone Lodge was well lighted, and Nancy wondered what was going on inside the house.

Suddenly the strange humming noise came to the girls' ears. As before, its source was elusive, seeming to be outdoors, and yet muffled enough to be inside. "It might be some sort of generator in the house," said Nancy. "But I shouldn't think we'd notice it from here." The two girls listened intently but still could not figure out the exact location of the sound.

Cecily showed signs of apprehension. "We're pretty close to the place where that phantom boat appeared," she told Nancy. "Just in case there's something dangerous about it, don't you think we should leave?"

Personally Nancy would have liked to stay, but out of consideration for Cecily, she agreed. They turned the canoe around and began to paddle back toward the cottage. Nancy kept looking over her shoulder, hoping the apparition would appear. Cecily, on the other hand, was wishing just as hard that it would not. The lake remained dark.

When they reached the cottage dock, Nancy glanced up. She glimpsed a man's shadowy figure moving off among the trees around the cabin.

"The prowler!" Nancy thought.