The grimoire known as The Key of Solomon is real. Probably written in the fourteenth or fifteenth century, it became hugely popular, although it continued to exist largely in handwritten manuscript form until late in the nineteenth century, when it was finally printed. There was a very real upsurge of interest in grimoires, or magic handbooks, in the nineteenth century. Most of those that became popular dated back to the Renaissance, for reasons Abigail McBean explains to Hero.
London’s vibrant molly underground—with its accompanying dangers of extortion and prosecution—was essentially as described here, although more vibrant in the eighteenth century than by the early nineteenth.
The Black Brunswickers were a real volunteer corps raised by Duke Frederick William, Princess Caroline’s brother, to fight in the Napoleonic Wars after the French occupied his duchy.
The life of London’s crossing sweeps was as described here, with these biographical portraits being loosely based on some of those recorded by Henry Mayhew. Mayhew’s work, which appeared midcentury, also serves as the inspiration for the collection of articles Hero is writing. Some of the crossing sweeps did indeed go to the Haymarket after dark, where they played a part in supplying girls to gentlemen in carriages.
The Abbey of St. Saviour in Bermondsey, Southwark, had almost entirely disappeared by the beginning of the nineteenth century. Besides the lay church (which still stands), all other traces vanished somewhere between 1804 and 1812. Since there is some dispute as to when, precisely, the gatehouse and its attached structures were demolished, I have taken the liberty of using them here