The Buntings went to bed early that night.

But Mrs.Bunting made up her mind to keep awake.

She was set upon knowing at what hour of the night the lodger would come down into her kitchen to carry through his experiment, and, above all, she was anxious to know how long he would stay there.
But she had had a long and a very anxious day, and presently she fell asleep.
The church clock hard by struck two, and, suddenly Mrs.Bunting awoke.

She felt put out, sharply annoyed with herself.

How could she have dropped off like that?
Mr.Sleuth must have been down and up again hours ago! Then, gradually, she became aware that there was a faint acrid odour in the room.