Then the man smiled, and his smile was a shock, for it was all on one side, going up in the right cheek and down in the left.
There was nothing, rationally speaking, to scare anyone about this.

Many people have this nervous trick of a crooked smile, and in many it is even attractive.

But in all Syme's circumstances, with the dark dawn and the deadly errand and the loneliness on the great dripping stones, there was something unnerving in it.
There was the silent river and the silent man, a man of even classic face.

And there was the last nightmare touch that his smile suddenly went wrong.
The spasm of smile was instantaneous, and the man's face dropped at once into its harmonious melancholy.

He spoke without further explanation or inquiry, like a man speaking to an old colleague.
"If we walk up towards Leicester Square," he said, "we shall just be in time for breakfast.