“Well, then we’ll just have to go without you,” said Teddy.  “But it would be lots more fun if you’d come.”  This last was said to Billie and for her ear alone.

That afternoon the girls watched the boys down the road till they were out of sight, then turned back to the house with a strangely lonesome feeling.

“You know,” said Violet, pausing on the doorstep and looking back at the girls with a rather sober face, “I have a sort of feeling that something’s going to happen.”

“Well, you’d better get rid of it right away,” retorted Laura.  “We don’t want anything more to happen—­especially when the boys are away.”

This time Violet proved to be right.  Something did happen.  It was after dark, the boys had not yet got back from the village, and the girls were setting the table in the kitchen—­they had never found the courage to eat in the gloomy dining-room—­when Violet set a dish down on the table with a bang that made the girls start and look at her in surprise.

As for Violet, she was too scared to speak for a moment.  Then she stammered out: 

“The strange motor car!” she said, while Billie and Laura stared at her.  “I thought I heard it before—­”

“Sh-h,” cried Billie, and they listened, hardly daring to breathe.

There was the same strange humming sound that had so startled them on their first night in the house, only this time, instead of coming from a distance and passing by, the noise seemed to get louder, then softer, louder and softer, as if whatever it was were approaching and retreating at regular intervals.

At that moment Mrs. Gilligan came into the room, and the girls called to her to listen also.

“That?” she asked, with a little laugh.  “Why that’s an automobile of course,” and started for the front door.  “Only I must say it’s behaving mighty queer.”

But when they opened the door and looked out into the rocky road there was no sign of an automobile, and yet the humming sound still kept on.

As they listened, wide-eyed, the noise grew softer and softer and gradually died away in the distance.

The girls looked at each other wonderingly.  Then it was Billie who offered a solution.

“Mightn’t it be an aeroplane?”

“An aeroplane in this part of the country?” Laura was inclined to scoff at the idea, but Mrs. Gilligan and Violet both stood up for Billie.

They were about to enter into a heated argument when they saw the wagon that had by this time become familiar to them coming down the road with the boys seated in it or hanging to it in characteristic attitudes.

The girls ran out to them and deluged the lads with questions before they had time to learn what it was all about.

“A motor car?” asked Chet.  “No, we didn’t pass a soul on the way up here.”

When the girls had poured into their interested ears the story of the queer humming sound that had just repeated itself, they agreed to one man to Billie’s suggestion that it was very probably an aeroplane.