A nightmarish allegory
This story begins one way and then winds up being a different story entirely as plot-twist after plot-twist change the flavor of the book, for better or worse. The original story looks like an allegory about bad parenting. Tempted by the fun of their youths, two young parents escape their parental responsibilities to enjoy a night without the child. They leave the baby alone and go next door for a party. While away, the child is kidnapped. They are unable to explain what happened, making the detective suspicious of them. It looks like an allegory on why not to leave one's baby unattended to go to a party.
The failed ransom
When Anne gets the five million dollars for a ransom, the couple takes another chance. This time, it isn't their lack of responsibility that they prove to the reader; it is that secretly, they are not big fans of the law or due process. Marco meets with the kidnapper in the night and is allegedly assaulted and robbed. The failed ransom leads to a five million dollar deficit, and still no sign of their poor baby. The failed ransom proves various character faults in the couple.
The traitor
Marco turns out to be a traitor in the most archetypal manner. He not only failed his responsibilities, but as the officer of the law suspected, he is secretly the mastermind behind the kidnapping. His symbolism lines up with the archetypal traitor, because he trades away his loyalty to his family for money. This is a betrayal for money akin to Judas Iscariot. Now, that seems apparent for one section of the novel, but after a confrontation between Marco and Anne, the reader sees that, again, things are more complicated than they seem.
Cynthia as a femme fatale
Anne thinks her husband is sleeping with Cynthia. That would make her a femme fatale because she is breaking up a marriage by luring the husband, and also because she ends up condemning Marco. She discovers footage of him stealing the baby, which means that she has an accurate understanding of his character. The clarity she has about Marco's character, the power she holds in his life, and the motif about Marco cheating on his wife with her all make her a femme fatale character.
The secret reason
Marco is secretly motivated by a valid reason (not really, but in the context of the novel it seems that way) for threatening the wellbeing of his child and marriage. Secretly, Anne's own father is to blame. Because he has enormous wealth and power, he does not consider Marco a suitable spouse for Anne, and when business seems like it would be expedited by exploiting Marco, he does it. He starts a threatening and exploitative business relationship with his son-in-law that precipitates this whole child-stealing narrative.
