She was ready, crouched close to the window of her room, when the signal came, but first she was not sure, because the sound was as faint as a memory.

Moreover, it might have been a freakish whistling in the wind, which rose stronger and stronger.

It had piled the thunder-clouds higher and higher, and now and again a heavy drop of rain tapped at her window like a thrown pebble.
So she waited, and at last heard the whistle a second time, unmistakably clear.

In a moment she was hurrying down to the stable, climbed into the saddle, and rode at a cautious trot out among the sand-hills.
For a time she saw no one, and commenced to fear that the whole thing had been a gruesomely real, practical jest.

So she stopped her horse and imitated the signal whistle as well as she could.