Mary (Elle Fanning) is a ghost girl who has been obsessed with ghosts and monsters since she was a child. She inherited her parents' advanced ideas and has an independent, strong and unruly personality. In order to give her daughter a better education, Mary's father sent her to the home of his friend William (Derek Riddell), where Mary met the young poet Shelley (Douglas Booth) who was full of melancholy. Mary was soon fascinated by Shelley. When she decided to elope with him to London, Mary discovered that Shelley already had a family. However, Mary didn't care about these. She firmly chose to be with Shelley. Because of betraying his family, Shelley lost the financial support from his father. Poverty did not break up him and Mary. What broke their relationship apart was Shelley's infidelity.