May 1816, Villa Diodati, Lake Geneva.
Mary Shelley, eighteen-years-old, has fled London with her lover Percy Shelley and her pregnant, unwed sister, Claire. Mary is tormented by Shelley's infidelities, haunted by the loss of their baby daughter and suspicious of her sister's intensions.
Geneva promises a new start.
But far from being a refuge, the summer is freakishly cold and stormy, skies shrouded with volcanic ash, the villa enveloped in superstition. Mary finds herself trapped in an endless cycle - dark afternoons of spirit-raising and ether-taking with their glamorous neighbour, Lord Byron. and his handsome but unnerving doctor, Polidori.
Once Byron proposes a ghost-story contest, an even stranger atmosphere descends. One in which passion mingles with fear, and the living confront the dead.