1816, Villa Diodati, Lake Geneva. A summer storm is brewing.

Mary Shelley, eighteen years old, has fled London with her lover, Percy Shelley, and her step-sister, Claire. Mary is tormented by Shelley's infidelities, haunted by the loss of their baby daughter and suspicious of her sister's intentions.

Geneva promises a new start.

Forced to wait out rain and thunder, Mary is locked in a villa with Shelly, her infuriating sister, and the infamous Lord Byron. But far from being a refuge, the summer is freakishly cold and stormy, skies shrouded with volcanic ash. Whilst waiting for the air to clear beyond their villa's walls, madness and salacious scandal take root indoors. Haunted by repressed desires and the spectres of their pasts, Byron suggests each write a supernatural tale.

Mary has an idea . . . From her fervour, the tale of Frankenstein is born.