I decided to investigate.
I looked out the living room windows into the darkness. Nothing.
I looked out onto the deck into darkness. Nothing.
I turned on the deck lights. Nothing.
I went to the entry, peered through the window at the little lit deer, and something appeared. On opening the door, I found tracks -- lots and lots and lots of them.
Tracks emerged from or disappeared into the yard toward the street, and into the scrubby clearing or trees toward both neighbors' houses, into the darkness alongside my own house, and straight across the length of the porch, where the scooped snow undulated in waves.
I do not know who visited, and I do not know where they went, but I do hope two things: A/ that they did not find shelter under or in my house, and B/ that they do find a warm place for the night.
Addendum: Immediatly after pressing Publish, I looked for the cats and found both of them on the chair, their heads parting the curtains, noses pressed to the window. Looks like the little one isn't so afraid if the big one is with her.