This has been bouncing around in my head for a while, and I've already got two variations on this progressing, but it's such fun I thought I should open it up to other partners.
It's sort of a ghost story--woman loses husband, mourns him for years, and finally meets him again...except that he's been reborn as a woman. The good
news is that, er, she has all of his memories. The bad news is that she's eighteen, homeless, and clearly interested in taking up where they left off the first time.
Drama and romance ensue.