But another part of her mind seemed to be working independently, asking her insistent questions.
The place seemed to her alive with alien presences, and once she caught herself listening--which was absurd, for, of course, she could not hope to hear what Mr.Sleuth was doing two, if not three, flights upstairs.

She wondered in what the lodger's experiments consisted.

It was odd that she had never been able to discover what it was he really did with that big gas-stove.

All she knew was that he used a very high degree of heat..