The door was shut, but not locked, as I had left it.

I feared to wake her mother, who has been more than usually ill lately, so threw on some clothes and got ready to look for her.

As I was leaving the room it struck me that the clothes she wore might give me some clue to her dreaming intention.

Dressing-gown would mean house, dress outside.
Dressing-gown and dress were both in their places.

"Thank God," I said to myself, "she cannot be far, as she is only in her nightdress." I ran downstairs and looked in the sitting room.