Someone who had visited my www.timetowrite.com site e-mailed me with an unusual request: he was having problems coming up with a plot for a script and wondered if I had any ideas... Well, normally I get paid quite a lot of money for doing that, but I did pass along to him a technique that you might find useful as well. He wanted to write something with a character on some kind of quest, set in a particular historical era, so this is what I wrote:
I suggest that you look at the story lines of movies you have really enjoyed and that have been successful,that have a quest kind of a story, and consider how they would be changed if they were set in the era you have in mind.
Just as an example, let's take "ET." The log line might be something like this;
A lonely little boy tries to shield an alien from the authorities and help him get back home, and along the way learns the meaning of true friendship.
Now if you were to transplant that to your era, who might be a fugitive? Not an alien, but maybe a criminal, or someone with dangerous political ideas, etc. Who might befriend him? It doesn't have to be a child, although it could be. Who would be the bad guys after the fugitive? How might the life of the person trying to help him (or her) be endangered?
This may seem like stealing a plot, but by the time you have finished adapting it to your era it will come out very different anyway.
By the way, this works in the other direction, too: the plot of a historical novel can be updated and in the process can yield a new story.