The crime
Various, including organized-crime witness tampering, Volstead violations, subway lechery, and many more in the first half of the 20th century.

The story
The Girls Who Fought Crime: The Untold True Story of the Country’s First Female Investigator and Crime-Fighting Squads is, predictably, more about the girls than the crime — and it’s really about one “girl,” Mary “Mae” Foley, and her determined rise within the ranks of a resistant and sexist New York Police Department beginning in the 1920s. It’s comparatively short — barely 200 pages, including endnotes and biblio — and it moves right along, so I finished it in a short-hop plane ride. And it’s fine; it’s even striking in a couple of spots. Maj. Gen. Mari K. Eder mostly doesn’t try to do too much, so a description like “the gassy, pouting music from the Bund’s oompah band,” playing at an American Nazi rally Foley is obliged to attend undercover, stands out nicely.

But…I said Eder mostly doesn’t try to do too much. Sometimes, Eder has to do everything, because one of the figurative crimes here is that there just isn’t that much archival material available on Foley: