Dark Streets is an investigative, horror role-playing game written by Peter Cakebread and Ken Walton and published by Cakebread & Walton.
Source: Wikipedia, "Dark Streets (RPG)", available under the CC-BY-SA License.
From publisher blurb:
London, 1749: A city of vice, crime and misery. Gangs of ruffians rule the streets, unopposed. Brothels proliferate. Child-beggars starve in filthy gutters. Corrupt night-watchmen and thief-takers turn a blind eye to wrong-doing. And dark creatures lurk in back alleys, called from beyond by the desperate with nothing left to lose.
But there is a new force on the streets of London; for the author and magistrate Henry Fielding has teamed up with his brother John to form the city’s first police force – the Bow Street Runners. The Fieldings have persuaded parliament to fund their crime-fighting endeavour, but they know that there is something behind the vice – for John Fielding’s blind eyes can see things that others cannot – things that man was not meant to know.