Everything is related to ground but technically a bad device is a load issue. Make sure you take the light bulbs out. if it were me I would that the switches on the circuit apart first then the receptacles. Start with the box closest to the panel and work your way out. if this happend while it was raining I would check any outdoor lights first.

and be careful a multimeter without true rms will pick up inductive current and give you goofy readings.

One other thought when you disconnect the line from the panel check the voltage of the disconnected line because you may have a double feed.