The Film: Meryl Streep and Jeremy Irons play Anna and Mike. They're actors playing the parts of Sarah and Charles in a film adaptation of The French Lieutenant's Woman. It's a metafictional party!

The Affair: In the film within the film, Sarah is a mysterious loner - the so-called "French Lieutenant's Woman" - and Charles fancies the pants off her.

He manages to free himself from the shackles of Victorian society in order to pursue his dream woman. Scandal ensues. 

Long-Term Relationship? Sarah is a wild one. She will not be tamed or domesticated.