Any occult or supernatural elements?
The occult will often play a central role, as it does in history (Philadelphia’s “black widow” murders) and in the literature (even the Op tangled with an evil cult in The Dain Curse) but, true to the game’s inspirations, the personal and social power of the supernatural is nasty enough without giving it literal power as well. Magic is not real in Fly From Evil as written, to maintain the integrity of mystery plots. The genre sourcebook includes material exploring the superstitions and occult traditions of some of the principal ethnic groups, though, to give grifters something to work with (or GMs in the mood to run a literal-occult variant).