Set in two intertwined timelines, the story alternates between Victorian England and contemporary 1980s. In the Victorian era, Charles Smithson, an engaged gentleman of privilege, becomes captivated by Sarah Woodruff, a melancholic woman known in the community as "The French Lieutenant's Woman" due to her scandalous past with a French officer. His obsession with Sarah leads to a complex and forbidden relationship that challenges the societal norms and expectations of the time.

In the contemporary timeline, actors Mike and Anna are filming a movie about Charles and Sarah while engaging in their own illicit love affair. Their off-screen romance mirrors the turbulent relationship of the characters they portray, blending reality and fiction. As the narrative unfolds, parallels between the lives of Charles and Sarah and those of Mike and Anna become clearer, illustrating the timeless nature of love, desire, and societal constraint.