A couple in Mason City woke up to a fire in the attic of their home.
The Mason City Fire Department responded to a call shortly before 8 a.m.
It took them about an hour and a half to extinguish the fire.
Investigators determined it had actually been smoldering all night long while the tenants were asleep. They had extinguished a grease fire on the stove the night before, but were unaware the flames had traveled up a vent and into the attic and ignited the insulation.