These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: Phryne is possessed by Isis in Death By Wicket. This has never come up again, even when she wears a similar outfit in a later book.
Canon Sue: Arguably, Phryne herself for every description of her that points out how beautiful she is...
Plus, she's always right, she gets away with everything, and she's incredibly superior. She does make up for it by being quite a decent person, though.
Fridge Brilliance: In the end of Ruddy Gore, the killer is revealed to be Leonard Brawn, the carpenter, who was furious about how much disrespect and bullshit he and the other technicals (tradesmen) got from everyone else. In particular, he says 'Nobody notices technicals'- and Phryne didn't either, only considering the actors as suspects. Guess he was right.
Murder and Mendelssohn has a very ordinary-sounding title, until you realize that it's a clue: not only are there murders involving a choir singing Mendelssohn, but the murders were because of Mendelssohn's music- specifically, the murderer was a Mendelssohn purist who disliked the way the victims butchered the music.
Fridge Horror: As of the latest books, it's 1929. The Great Depression is on the way, and after it is World War Two: Tinker would be old enough to have fought, and Jane, who wants to be a doctor, might well have ended up as a field surgeon, the way Doctor MacMillan did.
Fridge Logic: What the hell does Phryne do with all of those dresses? With the way she acquires them, you'd think her wardrobe wouldn't be able to take any more.
In Ruddy Gore, a weight is dropped from a large height onto the stage it was hanging above, intended to hit Phryne or the lead actor. Instead, it hits Prompt, who is crushed. Thankfully, no description is given.
Jane's story. She was hypnotized, she saw her grandmother commit suicide, and she was sent to a brothel- and then she saw a woman hanged on the way. Thank God Phryne rescued her.
Lin Chung being kidnapped by pirates.
The beginning of Blood and Circuses: A man is stabbed, and the blood ends up dripping through the damaged ceiling... and landing in his landlady's cup of tea. She only realizes this after she finished it.
They Wasted a Perfectly Good Plot: Madame Selavy from Dead Man's Chest, who is an incredibly interesting character but does nothing important and raises a lot of questions that don't get answered. Damn it.
Toy Ship: Jane and Kiwi in Dead Man's Chest, mainly due to their shared love of science.
Values Dissonance: Oh, boy. Given that this is set in the 1920's, there's truckloads of dissonance. Casual sexism and racism, blatant homophobia... Phryne thinks more like a modern reader than a normal woman of the 20's, but she's the exception, not the rule.
In Death Over Wicket, Phryne runs into several cases. Clarence Ottery says that he's a black sheep because his uni course is Arts, not Medicine, and Phryne thinks 'Seriously?' In another, Joss basically says that whores are cheap and worthless, and Phryne has to resist the urge to hit him because she's investigating the disappearance and possible death of Dot's sister, an ex-whore.
What an Idiot: Ms Prout in Away With The Fairies decides to answer the really dangerous letters sent to the magazine she works for. This sounds harmless, except that she has absolutely no knowledge about any of the things she's talking about. Combine this with her pompous morals, and her letter-answering career ends up nearly destroying a marriage, getting a woman with a very sick child sacked and indirectly leading to the suicide of a woman suffering from post-natal depression- and those are just the ones we hear about.