Sh*t! ~ That happened to us when we had a chimney related problem with a stack that had been sealed off thirty years ago. It happened last year and we are still finding soot on books etc. It smells of soot for months after you think you have cleaned it all up. Soot only fell into one room but the residue went right through the house in an unseen cloud until everything was coated in a fine film of soot..... It was several days before we noticed just how far it had got. Even white shirts and stuff in wardrobes and drawers that were closed ended up having to be washed.