The Hidden Staircase by Carolyn Keene

the mansion. She climbed the stairs and for a second time that night undressed. Helen had already gone back to sleep, so Nancy crawled into the big double bed noiselessly.
    The two girls awoke the next morning about the same time and immediately Helen asked for full details of what Nancy had learned outdoors the night before. After hearing how her friend had been stopped by the guard, she shivered.
    “You might have been in real danger, Nancy, not knowing who he was. You must be more careful. Suppose that man had been the ghost?”
    Nancy laughed but made no reply. The girls went downstairs and started to prepare breakfast. In a few minutes Aunt Rosemary and her mother joined them.
    “Did you find out anything more last night?” Mrs. Hayes asked Nancy.
    “Only that a police guard named Tom Patrick is on duty,” Nancy answered.
    As soon as breakfast was over, the young sleuth announced that she was about to investigate all the outbuildings on the estate.
    “I’m going to search for an underground passage leading to the mansion. It’s just possible that we hear no hollow sounds when we tap the walls, because of double doors or walls where the entrance is.”
    Aunt Rosemary looked at Nancy intently. “You are a real detective, Nancy. I see now why Helen wanted us to ask you to find our ghost.”
    Nancy’s eyes twinkled. “I may have some instinct for sleuthing,” she said, “but unless I can solve this mystery, it won’t do any of us much good.”
    Turning to Helen, she suggested that they put on the old clothes they had brought with them.
    Attired in sport shirts and jeans, the girls left the house. Nancy led the way first to the old ice-house. She rolled back the creaking, sliding door and gazed within. The tall, narrow building was about ten feet square. On one side were a series of sliding doors, one above the other.
    “I’ve heard Miss Flora say,” Helen spoke up, “that in days gone by huge blocks of ice were cut from the river when it was frozen over and dragged here on a sledge. The blocks were stored here and taken off from the top down through these various sliding doors.”
    “That story rather rules out the possibility of any underground passage leading from this building,” said Nancy. “I presume there was ice in here most of the year.”
    The floor was covered with dank sawdust, and although Nancy was sure she would find nothing of interest beneath it, still she decided to take a look. Seeing an old, rusted shovel in one corner, she picked it up and began to dig. There was only dirt beneath the sawdust.
    “Well, that clue fizzled out,” Helen remarked, as she and Nancy started for the next building.
    This had once been used as a smokehouse. It, too, had an earthen floor. In one corner was a small fireplace, where smoldering fires of hickory wood had once burned. The smoke had curled up a narrow chimney to the second floor, which was windowless.
    “Rows and rows of huge chunks of pork hung up there on hooks to be smoked,” Helen explained, “and days later turned into luscious hams and bacon.”
    There was no indication of a secret opening and Nancy went outside the small, two-story, peak-roofed structure and walked around. Up one side of the brick building and leading to a door above were the remnants of a ladder. Now only the sidepieces which had held the rungs remained.
    “Give me a boost, will you, Helen?” Nancy requested. “I want to take a look inside.”
    Helen squatted on the ground and Nancy climbed to her shoulders. Then Helen, bracing her hands against the wall, straightened up. Nancy opened the half-rotted wooden door.
    “No ghost here!” she announced.
    Nancy jumped to the ground and started for the servants’ quarters. But a thorough inspection of this brick-and-wood structure failed to reveal a due to a secret passageway.
    There was only one outbuilding left to investigate, which Helen said was the old carriage house. This was built of brick and was fairly large. No