And Billie, after a moment during which she seemed undecided whether to laugh or cry, presently joined him.

“A dog!” gasped Chet, when he could get his breath.  “Come here, old man, and let’s have a look at you.”

The dog that had caused all the disturbance came forward at Chet’s command and stood looking up at them, his handsome brush waving genially.

As the light of a street lamp shining through the window fell upon him, Billie uttered an exclamation.

“Why, it’s Bruce—­Nellie Bane’s collie,” she cried.  “How in the world did he ever get in?  Come here, Bruce, old boy, and explain yourself.”

Obediently Bruce went over to her and laid a cold muzzle in her hand, his soft eyes looking lovingly into her face.  For Billie had made much of Bruce on her frequent visits to Nellie Bane, and the dog, with the instinct of his kind, had developed a great liking for her—­though the first in his loyal dog’s heart was Nellie Bane, his mistress.

“You’re a great one!” Chet scoffed.  “You get a fellow all worked up to catch a burglar, and then you produce a dog.  I think you did it on purpose.”

“Yes, and I suppose I scared myself half to death on purpose too,” said Billie sarcastically, as she patted the dog’s great head.  “Where are you going?” she asked, as Chet started back into his room.

“To put this thing where I got it,” he explained, holding up the pistol from which Billie shrank back.  “Don’t imagine we’ll have any further need of it to-night.”

“Wait a minute,” ordered Billie, and Chet turned back surprised.  “We haven’t found out yet how Bruce got in,” she explained, looking fearfully over her shoulder, for the effects of her fright had not quite left her yet.  “Don’t you think we’d better take that along while we look through the house?  We must have left a door or a window open somewhere.  Bruce couldn’t have come through the wall, you know.”

“Something—­I don’t know what it can be—­makes me agree with you,” returned Chet sarcastically, but he turned to the stairs nevertheless, “Come on,” he said.  “If we have left a window open it is high time that that window was shut.  Go ahead, Bruce, and show us where you got in—­that’s a good old boy.”

At the best it was rather an eerie business—­searching through the empty house at that time of night—­and it was especially nerve-trying for Billie after the fright she had had.

And then they found it.  The French window that opened from the dining-room upon the porch was swinging wide open—­a wonderful invitation to enter for any sneak thief who might happen to pass that way.

Billie shivered again as Chet, with a final pat, put Bruce outside and closed and locked the window.

“There, I guess we won’t have any more visitors to-night,” he said, as they started through the dark living-room to the stairs.

“Let’s hope not,” returned Billie fervently.