Like Nicole Kidman and David E. Kelley's previous film for HBO, "Big Little Lies," their drama "The Undoing" (opens in new tab) is based on a beloved book: "You Should Have Known" by Jean Hanff Korelitz in "The Undoing" (opens in a new tab). The series is a looser adaptation of the original than "Big Little Lies," but the characters in "The Undoing" (opens in new tab) are based on those in "You Should Have Known," and at least the first episode closely resembles the original. Both the book and the series revolve around Grace and Jonathan (opens in new tab), a therapist and pediatric oncologist, respectively, whose lives are torn apart by a horrific crime. There are spoilers for episodes 1-5, "The Undoing," and for the book "You Should Have Known," ahead.

Ahead, I will list some of the most notable similarities and differences between "The Undoing" and its source material (which is a great book in its own right and worth a read, whether or not you enjoy the series).

The central family in "The Undoing" has the same name and the same characteristics as the family in "You Should Have Known". Grace, a therapist born and raised in New York City, specializes in relationship therapy and believes it is her duty to tell her clients that they are in a prison of their own creation. Then there is Jonathan, a charming pediatric oncologist who is Grace's husband and Henry's father. Henry, meanwhile, is a violin student at Rearden, a private school in New York City whose tuition is paid for by Grace's wealthy father.

However, other characters in The Undoing, especially Sylvia (Lily Rabe), Grace's other friends at Rearden, and Grace's father (Donald Sutherland), are portrayed quite differently than they are in the book. Grace's father, for example, is a large man who appears to be single in the series, while in the novels he is quite quiet and happily married to his second wife. There are also several characters in the book who do not appear in the film, such as Grace's former best friend, partly because the book is set in a beach house and the series is set in New York City.

This is an important difference. Elena in the Jean Hanff Korelitz version is called Malaga Alves and is much younger and less bewitching than in the HBO version. Malaga Alves appears to be similar to "Elena" in that she is also the mother of a young son and a young daughter, but Elena is a very different personality: Elena has agency, while Malaga does not. Malaga also does not exhibit the sexually provocative behavior around Grace that is depicted in The Undoing.

There are several possible reasons why Malaga became Elena. First, Malaga has been accused of being a Latino stereotype (opens in new tab). Second, the show is a gorgeous, glossy television show, and Elena is a young, gorgeous, glossy woman who literally gets naked in the second scene. Third, Malaga has only a small role in the book, and it is immediately apparent that Elena is an important character in the series.

Both the book and the film use the violent death of Malaga/Elena, the woman with whom Jonathan had an affair, as the catalyst for everything that follows. In the book, Malaga is stabbed to death; in the series, Elena dies from a blow to the head, but both are violently killed one night and their bodies are found the next morning by their young son.

The series begs the question: who killed Elena? Was it Jonathan or someone else?". It is clear early in the novel that Jonathan murdered Malaga/Elena, and he confesses in a letter to Grace at the end of the book. He also remains on the run for almost the entire novel, which indicates his guilty conscience. (At the end of the book, he is caught overseas and extradited back to the United States.) The book essentially concludes with the conclusion that Jonathan is a sociopath.

However, the series takes a very different approach, hinting at the possibility that Jonathan is innocent. He points the finger at Elena's husband, Fernando Alves (Ismael Cruz Cordova), who is a much larger figure than he is portrayed in the novel, and later in the series suggests that Grace and Henry may be the culprits. Not so in the novel: Fernando only appears when the detectives tell Grace that he has a solid alibi for the night he murdered his wife, and since the novel is told from Grace's perspective, it is clear that she is not the killer. No one suspects Henry as the killer.

Another character who does not appear in the book is defense attorney Haley Fitzgerald (Noma Dumezweni). Jonathan in this book does not have a defense attorney. This is because there is no trial and Jonathan escapes capture until the very end of the book.

Director Susanne Bier says (opens in new tab) Marie Claire: (opens in new tab) "It was always going to be Jonathan who killed Elena. The series uses books (as inspiration) in the first two episodes, but as a kind of conceptual framework. The idea of "regulating the truth" and "massaging the truth into what you want it to be" is a very important issue, and we all felt we were doing a really fun, really funny hodgepodge of hodgepodge, but the core of it was the philosophy of that (book).

Something that seems innocuous at first but later becomes clear that speaks volumes about the book: Jonathan's dislike of dogs In "You Should Have Known," Jonathan does not allow Henry to have a dog. This is because the dog he had as a child ran away in front of Jonathan, and the incident turned Jonathan's family against him.

This same story is told in the series: Grace tells her son that Jonathan was estranged from his family after the death of their dog. However, when Grace eventually speaks with Jonathan's mother, she is told a very different story. It was not the dog, the mother reveals. It was his sister, and her death was Jonathan's fault.

This is also true in the novel, but with some differences. In the novel, it is the younger brother, who was left with the younger brother when he came down with the flu. Jonathan locked his brother out in the cold and left him to get sicker.

The title "You Should Have Known" is a reference to a self-help book Grace is writing. This is one of the central conceits of the book: that Grace, a woman who is writing a self-help book that specifically describes what she "should have known" about the core characteristics of her partner before she was linked to him, will find herself in her current situation. Grace in this book lives by the central tenet of the self-help books she writes: know the person's worst traits and what you are getting yourself into before you get married.

The self-help book is omitted from the series entirely. Grace in the series is in the same profession and has a "should have known" attitude toward bad relationships, but no books.

In both the book and the series, Grace and Henry flee to her family home upstate after the New York media grab the story. In the book, they stay there permanently, Grace is reunited with an old beloved friend, her father comes to visit, Henry likes his new school, and there are hints that Grace finds a new love.

In the series, they return to New York within an episode.

There is no great mystery as to why these changes were made. Jonathan in this film is American and was born and raised a few hours from Grace.

In the series, of course, Jonathan is played by Hugh Grant. There is no doubt that Hugh Grant can do an American accent, but I must say that it is a major turn-off to see Hugh Grant do an American accent and try to make it seem like it is normal. It would make much more sense for Jonathan in this series to be British and settled in New York City.