This was my first introduction to Inspector Blunt. I am so used to the foibles of Hercule Poirot and the little eccentricities of Miss. Marple that Blunt's straightforwardness was a surprise!
All the characters are not what they seem - they all have a hidden agenda and the plot is complicated (but that is normal for an AC book). At the same time the characters seem typical the gold digger second wife with the eye on the main chance, the put down trodden on first wife humble and subservient, the rich mother, a doting "son", and the various hangers on who seem to drift towards the story but are all very relevant.
A bit that struck me was that it is quite true that unlike in a murder of passion, murders of AC are all premeditated and planned so that the murder actually starts with a series of apparently unconnected events long before the actual event. Apart from that the solving of the murder also depend on totally irrelevant features and people who may have been accidentally passing by, dropping in or waiting nearby for something or the other totally disconnected from what is happening underneath their noses!
A short story and the twist in the tale is typical of Dame Christie's writing. It was just what I needed.