Braving the elements, not waiting for the blistering sun to go away, I went ahead and 'gotter done.' I have tested all the receptacles on this circuit and, further, just as a 'final insuring measure,' turned off all breakers but the one involved--still no joy. I'm now at a loss as to what is on this once-before-working circuit that causes this interference with nothing else connected.
(Could it be this circuit is feeding an area of the house I'm not aware of? I don't think so, but just to be proof positive I will turn off all breakers but one--when my precious wife is missing from the home--and go through the house with a fine tooth comb, and my tester, and confirm this circuit extends only to the garage, back porch, and outside junction box.)
Any other ideas?