Cen-Tech Cable Tracer 94181 Just the tool I needed. Mystery wire found.

I had an outlet with no power. The hot, neutral and ground did not trace back to any wire in the breaker panel. This cable tracer did the trick of tracing the wire back through the walls and through the ceiling. The setup and operation was easy. I was able to penetrate drywall and detect wires at different distances from the receiver.
A quick note on the operation, turn the volume all the up at first and be sure to press the button to get a baseline for your project. I was able to turn down the volume some as I went along. In noisy environments, a headset or earbuds can be used with the supplied jack. I know I will be using this checker throughout my house on future projects.