Unable to sleep, Mary became possessed by the idea of a reanimated corpse. “I saw the hideous phantasm of a man stretched out, and then, on the working of some powerful engine, show signs of life, and stir with an uneasy, half vital motion,” she wrote. 

Aged just 18, she began writing the novel, about a scientist called Victor Frankenstein who devises a way to imbue life into non-living matter. The result is a nameless, giant monster, with translucent skin that “barely disguised the workings of the arteries and muscles underneath”. The creature escapes, and embarks on a murderous rampage. Frankenstein was born.

The Shelleys’ Bloomsbury home today looks decidedly un-spooky. The property on the site where they used to live has a brick facade, original wood floors and sash windows. A two-bedroom flat in the building is for sale with Dexters estate agents for £1.025m. 

The current owner has decorated with a welcoming array of house plants. Cyclamen spill over pots on the decking in the garden. 

But buyers with a Gothic bent, rest assured. St Pancras Old Church and its graveyard are only a 15-minute walk down the road.