Temptation may be a plot unto itself, but I include it here because presently it is hard to imagine any other motivation that would make a story. In our multi-cultural, diverse, non-judgmental (anarchistic – anything goes) society, the idea of forbidding love seems old fashioned. We have room for it all these days: black and white, Christian and Jew, gay relationships, may-December romances. So the Minister ran off with his secretary or the Governor his South American hottie – yawn. Heck, there is a television show about Cougars. So what?
Lolita can still raise some eyebrows. Incest, pedophilia, sadomasochism might still be “forbidden,” but for the most part, these days “forbidden is in the eye of the beholder.” For that reason, temptation is a good opening. If the participants are irresistibly drawn to each other, though they themselves believe it to be wrong, you may have a beginning.
Historically, forbidden love has been a powerful vehicle for exploring love and for exploring tragedy. Adultery (The Scarlet Letter) and affairs have been standard fare. Also, when two groups of people oppose each other and a couple find each other in the midst of that opposition, such a love is invariably tragic. Imagine a young American soldier and the daughter of a Jihadist. Imagine the Hatfields and McCoys. Imagine Romeo and Juliet.
Of course, it didn’t work out too well for Romeo and Juliet. They were in love from the beginning (connected) but all the forces in the world conspired to keep them apart (separated). They got together in the end (reconnected), almost. I suppose that is why it is a tragedy, but Romeo and Juliet does follow the basic love story plot pattern.
Another approach to this storyline might be called the impossible love. Both Casablanca and Cyrano de Bergerac touched on this. The Hunchback of Notre Dame did a better job because as disfigured as he was, he knew his love for Esmeralda was impossible. Of course, these days even monsters like vampires are seen as acceptable lovers (though there is some sense of forbidden love there, to be sure).
Also, keep in mind that social standing cannot be used in “forbidden love” as it might have been in the past. Yes, it was a scandal when Edward abdicated the British throne to marry that divorced American – and that had a basically happy ending, but these days would people really care?
Like the basic love story, the story of forbidden love begins with the chemistry of two people drawn together, irresistibly. In this case, though, the wrongness of the attraction or the impossible nature of the love must be made clear. Then comes the trouble.
Unlike the love story, the center of this work often shows the two people together and to some extent shows what is right about the pairing even in the midst of the wrongness. Often, it is not the world conspiring to keep the lovers apart so much as the fear that the world will find out, find them and force them to part.
Here is where all the plots are hatched, such as the plot to kill the spouse of the one that is married. Sometimes they work out. Often they don’t, but even when they do there are always consequences.
In the final act, the tragedy. Society does not like to lose. It is like our soldier and jihadist’s daughter. Even while he is under guard and facing a possible dishonorable discharge, she is being stoned to death. Sorry. This plot rarely, very rarely has a happy ending.