It's nearing Martian Mother's Day and Martin is feeling sad in not being with his mother on that day. He even projects a 3D image of her to make himself feel better. On the day, he runs into Miss Cora Darling, a spinster the spitting image of his mother. Martin wants to do something nice for his mother lookalike, so a worthless but sentimental ring she has appraised - the ring from a former lover - Martin temporarily turns into a valuable piece not thinking that she'd sell it to the jeweler, which is what she does. So to get the ring before it reverts back into being a worthless trinket and before the jeweler thinks he was swindled, Martin devises a plan to get the money from Cora by doing the work for which she needed the money, namely some structural renovations to her house, and re-buy the ring from the jeweler.
—Huggo