Because it came up recently-ish… 19th century Whitechapel was full of Eastern European Jews. There are modern walking tours of the area to see the Jewish sights.
My character engages with these Eastern European immigrants. The Jewish population in England increased from 46,000 in 1880 to about 250,000 in 1919. To quote the Jewish East End of London page, “The Ashkenazi immigrants were often illiterate, poor and regarded as an embarrassment by co-religionists already settled here. These Ashkenazi Jews had fled to the West as refugees from Russian persecution.” The Jewish population of London in 1899 was 135,000.
I don’t consider myself an expert on Jewish history! but I already I knew this from two particular sources, neither of which was particularly flattering: Dracula and Jack the Ripper. Yes, Jack the Ripper was terrorizing a poor Jewish immigrant community! There was graffiti at the time blaming the Jews for Jack the Ripper’s crimes, or at least for sheltering the killer. (See “The Goulston street graffito;” the police suppressed this because they feared it would lead to antisemitic riots.)
Dracula, well. Dracula is in many ways a reverse colonization narrative. There are apparently antisemitic remarks in the book that sailed right over my head because I’m not up on bigoted 19th century stage plays, but… the sly Eastern European count stalking the dark, foggy streets of London can be read as a representation of the influx of Eastern European immigrants, particularly those escaping Pogroms in the Pale of Settlement.
So, my characters know that Whitechapel has a reputation for “being Jewish” and seek Jews there. These characters are Yiddish speakers and eat Eastern European foods. There are lots of great photos here, including Yiddish newspapers and the like.