The cause of a fire that extensively damaged a Fond du Lac home Monday remains under investigation. Nobody was injured in the fire at 213 Military Road. When firefighters arrived early Monday morning the fire had quickly spread up the side of the house into the second floor and attic. Residents were alerted by smoke detectors and were able to safely escape the burning structure. One pet dog was rescued, a second dog is still unaccounted for. The Red Cross is assisting the family.