She knew she had reached the last step when her hands encountered wood, and she felt about till she touched the knob of the door.  It opened at her touch and she pulled herself in over the sill.

“Now the card,” she whispered, feeling in her pocket.

A gust of wind fanned her cheek and something clicked.

The door had blown shut!

CHAPTER XXI

DRAMATICS

There are pleasanter places to be at midnight than the dark room of a strange water tower, but Betty was not frightened.  She tripped over some tool as she felt for the door and discovered that she had lost her sense of direction completely.

“I’m all turned around,” was the way she expressed it.  “I must start and go around the sides, feeling till I come to the door.”

Following this plan, she did come to the door and confidently turned the knob.  The door stuck and she rattled the knob sharply.  Then the explanation dawned on her.

The door was locked!

Could it have a spring lock? she wondered.  Then she remembered a day when, on exploration bent, a group of girls had made the trip to the roof and the kindly Dave McGuire had taken a key from his pocket and unlocked the door of the little room for the more adventurous ones who wanted to climb up and see the inside.

“It was a flat key, like a latch key,” Betty reflected.  “The girls must have had the door unlocked for me to-night, but I don’t think they would follow me and lock it.  That would be mean!”

However, the door was locked and she was a prisoner.  It was inky black and at every step she seemed to knock over something or stumble against cold iron.  Gradually her eyes became accustomed to the lack of light, and she made out the outlines of something against the wall.

“Why, there is a window—­I remember!” she said aloud.  “I wonder if I can reach it.”

Cautiously she felt her way around and stretched up tentative fingers.  She could barely touch the lower frame.

Then, for the first time, Betty felt a little shiver of fear and apprehension.  It was close in the tower room, and the smell of oil and dead air began to be oppressive.  She had no wish to shout, even if she could be heard, a doubtful probability, for she had no mind to be rescued before the curious eyes of the entire school.

“I’ll get out of it somehow, if I have to stay here all night,” she told herself pluckily.  “Oh, my goodness, what was that?”

A tiny sawing noise in one corner of the room sent Betty scurrying to the other side.  She would have indignantly denied any fear of mice or rats, but the bravest girl might be excused from a too close acquaintance thrust upon her in the dark.  Betty had no wish to put her fingers on a mouse.

“How can I get out?” she cried aloud, a little wildly.  “I can’t breathe!”

In the uncanny silence that followed the sound of her voice, the sawing noise sounded regularly, rhythmically.  In desperation Betty seized an iron crowbar she had backed into on the wall, and hurled it in the direction of the industrious rodents.