It turns out his name is Jake and he had been missing since last weekend. Jake lives about 5 houses further down my street. I've written down his address in case he returns (and put it in my CATS file, the real paper kind).
I let her know that he had stayed in my yard by his own choice since Wednesday, but that I had let him in the basement at night and when it rained. She was very relieved that I had been feeding him and giving him plenty of attention.
She didn't know exactly how he got lost. I didn't think to ask whether he was strictly an indoor cat or not. From the way he stuck right at the deck door (and to me when outside), I suspect he is.
Well, it certainly was an interesting 5 days! I am SO relieved to have found Jake's owner. And it sure saved my taping up a lot more notices. ;) Having lost Tinkerbelle to "wanderlust", I know how upset and sad Jake's girl was feeling.
In celebration of this happy outcome, the cats and I are having shrimp and ham for dinner tonight!