So bad. First, very amateurish and bad writing. Many repetitions, everything is compared to everything else in an elaborate way for a writer to show off (abandoned like Mary Celeste), unnecessary detours to show how smart the author is when it comes to googling (who is was that killed the messenger? Or, that chap, Tigranes of Armenia). Lots of long and rare words used where shorter and more commonly used words would suffice, also, probably, to show the reader how smart the author was who knew all these long obscure words (and, of course, facts). Very long, awkwardly built sentences. Outlandish names that are very difficult to remember, reminiscent of bad fantasy fun fiction.
The writing is very uneven, jumping from topic to topic and from theme to theme, so often the meaning is ambiguous and intentions of the protagonists are unclear, for example, when miss Dimont calls the editor and tells him about the murder, the reply is "And he is not the only one who is dead", it sounds like a threat in the context, like her editor saying her "do this or that, or you are dead", when, in fact, really some other person is dead.
Second, the heroine herself is annoying and narcissistic. Also, very shallow. She goes around, interrogating people, often rudely, and, surprise surprise, when she barks her questions at them, they reply, why not tell her to go where the sun does not shine? She accuses people of all kind of things, and throws water in their faces, then she sincerely expect them to be "nice" to her and answer more of her questions. Moreover, when she asks a question, she never listens to the answer but starts answering instead of her interlocutors, and it's hard even to call "an answer", she is just talking about her fantasies and own agenda. So, it takes a long time for a person to answer a question and the dialogues are long rambling monologues of a "brilliant" Miss Dimont, interrupted from time to time by her own questions. She interferes with police investigation, destroys and tampers and withholds evidence from the police, then acts all superior. In fact, if she did not take evidence and tampered with it by carrying it around in her bare hands and giving it to other people to touch and carry, the case would not have lasted for longer than ten pages. In short, instead of a person who is smarter than the police, as the author intended, she rather looks like that classical busy body who does not have a clue and interferes to validate her own high opinion of herself. She interferes with other people's jobs, not just the police, probably an attempt to make her appear emphatic, but she always comes out of such interferences as a person who does not even know what she is talking about and who knows that she would not even change anything but rattles people to feel important. At the same time, she is so childish, for example, she is amazed that people in professional surroundings look and act differently than in private ones, it would have been acceptable in a child of ten, not in a mature, smart and sophisticated woman of a near retiring age.
Third, it's not even a mystery, there are no consequent cues pointing then to one person, then to another. It's a long rambling text consisting of random facts, narcissistic monologues of the main protagonist and somewhat cute descriptions of a seaside town.