An investigation is underway into the cause of a late-night house fire.  It was reported about 11:30 in the 9-hundred block of Portland Street.  When firefighters got there, they found flames coming from the rear of the one-story wood frame home and smoke everywhere.  The house was vacant at the time -- and in the process of being renovated.  Investigators have determined that the fire started in a bathroom in the rear of the house.