The murder of Merritt Monaco lies at the center of the tangled web of secrets, strained family relationships, and high financial pressure that embodies Elin Hilderbrand's The Perfect Couple. As it is finally revealed toward the end of the novel, though, not considered a murder at all, the death of Merritt was caused by Abby, Thomas Winbury's wife.
However, in the Netflix adaptation of The Perfect Couple, that explanation is very different and more straightforward: Abby premeditated the murder of Merritt because she did not want to disrupt the flow of money in her family.
While several possible motives for the murder are brought out both in the book and in the show, the root cause leading to Abby's decision is her fear that Merritt's pregnancy will slow down the family's access to their trust fund. Here are the motives behind Merritt's death, as depicted in the book and the show, The Perfect Couple.
Abby's motive: Safeguard the family fortune
In both the book and the Netflix series, The Perfect Couple, Abby's motive for Merritt's murder is linked with the trust fund that represents their family's future fortune. In the book, Abby is portrayed as saving her husband Thomas from the implications of Merritt's pregnancy.
If Merritt were to give birth to Tag's child, then the family's inheritance would be postponed for 18 years because the legal entity of the trust requires all children to first attain the age of 18 years before the money is accessed. This motive is rather apparent in the Netflix version.
Abby tries to get Thomas to kill Merritt so that the trust fund will not be delayed, but when he does nothing, Abby takes matters into her own hands. In the series finale, Abby crushes a pill into Merritt's drink and then drowns her so the pregnancy will never come to fruition.
When the truth comes out, Abby is put behind bars as Detective Nikki Henry puts the pieces of the puzzle together.
Tag's motive: Avoiding a scandal
There is also, in the book and the show, a possible motive for Tag Winbury, Merritt's lover and the father of her unborn child, to want her dead. Tag's affair with Merritt is a big threat to his marriage with Greer, not to mention the Winbury family image. Were the pregnancy to get out, it would be one scandal that could irreparably destroy the family's reputation.
While Tag is not directly involved in Merritt's murder, his relationship with her adds to the web of deceit and danger enveloping the Winbury family. In the Netflix series, of course, suspicion hangs on the very real possibility that Tag may have had a hand in Merritt's murder, but it is Abby who commits the act.
Greer's motive in The Perfect Couple book: Protection of family legacy
Another character in The Perfect Couple book with a possible motive for wanting Merritt gone is Greer Winbury, Tag's wife and the family's matriarch. Greer is very concerned with keeping her family's status intact and their good name from being ruined. However, she does not kill Merritt and learns that Abby killed her only later in the story.
Rather than turning Abby in, Greer keeps the secret, allowing her family's image to be protected rather than justice being served for Merritt. As in the series, Greer's part in the show is less central to the actual murder, although she is more or less concerned with keeping the family reputation intact as a more salient aspect of her personality.
She does nothing in The Perfect Couple novel to further any personal motives for a desire to see Merritt harmed, but her silence speaks volumes about what she values most.
In both the novel and the Netflix series adaptation of The Perfect Couple, the death of Merritt relates to complex motives relating to family, money, and long-kept secrets. The fact that Abby did not want to lose access to the family trust funds is a motive for killing Merritt so that the timeline of inheritance is not disrupted.
Whether subtly done like in the book or as bluntly as in the show, the death of Merritt is a tragic consequence of desperation to save the family's wealth and status in The Perfect Couple.