All the ground floor windows were shuttered tight, but upstairs, on the first floor (it was a two-storied house) I noticed a window with a light burning and the curtains not drawn.
All the ground floor windows were shuttered tight to prepare for the coming storm, but upstairs on the first floor I spotted a light in a window.
mnli hypothesis: All the ground floor windows were shuttered tight to prepare for the coming storm, but upstairs on the first floor I spotted a light in a window. premise: All the ground floor windows were shuttered tight, but upstairs, on the first floor (it was a two-storied house) I noticed a window with a light burning and the curtains not drawn.