This movie begins as a drama, and unfolds with a story about a true psycho.
It's not a spoiler to state that the "bad stepmother" is deranged. I don't think I have any "spoilers" in this review.
The murder of a wealthy man is how this begins. We know the stepmother is the killer. Within the first five minutes of this film, she meets with the two children of the man she killed. Her own son is also there to meet the two children.
To any street savvy person, much of what later takes place is obvious. This story is actually a theatrical drama about the elite in the world of street savvy people, in a culture where the dividing line no longer exists.
There are many important characters in this story. We even understand the posthumous character of the father, who chose someone out of the gutter that he felt could be his new wife.
There are the two siblings, a brother, obviously older, and very responsible, and a sister, who has many flaws and lives for the moment. The stepmother, her son, the lawyer who is executor, a maid, a private investigator, and a very quiet fiancee of the brother make up the bulk of the story. Two other very pivotal characters make brief appearances.
What really draws us in to the story is the older brother, the strength of the story. As an elite member of society, he has learned some street savvy, and it's obvious. His sister thinks she has street savvy, but doesn't. The brother is almost an "everyman" thrown into the situation of a wealthy man thrust into a world where there really is no protection from danger. What is perceived as "protection" is a facade that already most everyone knows is a facade. That's what makes it so easy for human monsters like the stepmother to become a very outspoken part of society.
This makes some events even more important to us later on. We're following the brother, whose instincts born of experience are correct. His fiancee is assisting him.
There is a parallel between the gold digging stepmother and the man's daughter. Both are venturing into the world with no cares. The stepmother is haggard, and one wonders how she fools so many people. Actually, haggard people are much more likely to "con" people than the elite realize. That's where two people in this story make fatal errors.
How does she fool him? How does she fool other characters? That's one thing this screenplay doesn't go into. Given another half hour, the writer and director might delve into that.
That's one of the strengths of this movie, to simply show the homicidal maniac for what a homicidal maniac is, and not try to gloss over it for the Beavis and Butthead crowd who want to identify with homicidal maniacs.
This movie does so by giving us the appearance of a parallel between characters, only to show that this parallel never truly existed. This film is one of those that has more than is evident at first glance.