All Her Fault: The Biggest Differences Between The TV Show And Book

Contains spoilers for "All Her Fault" 

Adapting a hit novel into a TV series is probably a fairly daunting task, but luckily for novelist Andrea Mara, her 2021 thriller "All Her Fault" was masterfully adapted by showrunner Megan Gallagher and her star, Sarah Snook (who also serves as an executive producer). Snook stars as busy but incredibly devoted working mom Marissa Irvine, who thinks nothing of picking her young son Milo (Duke McCloud) from a scheduled playdate with Jenny Kaminsky's (Dakota Fanning) son Jacob (Tayden Jax Ryan). When she arrives at the address Jenny provided, a woman answers the door who doesn't know anything about any playdate; worse still, Milo is nowhere to be found, and Jenny insists she never arranged the playdate in the first place. Before long, Milo is declared missing, leaving Marissa and her husband Peter (Jake Lacy) terrified and desperate for answers.

So what changed during the adaptation process? Honestly, not much! Actually, Gallagher's adaptation of "All Her Fault" manages to expand the world of Mara's frankly excellent novel without making the miniseries feel overstuffed or overly ambitious, and characters in the book who don't get a ton of play end up with their own major character arcs (including one absolutely excellent supporting player who's not in the boom at all). Here are five major differences between Andrea Mara's book "All Her Fault" and its 2025 Peacock adaptation.

Adaptations change settings all the time, especially when a story that's not set in the United States is adapted for the big or small screen. HBO's Liane Moriarty adaptation "Big Little Lies" helped popularize this creative choice — Moriarty, who hails from Australia, set her story down under only for the television series to take place in Monterey, California — and that happens in "All Her Fault."

Andrea Mara — who, again, wrote "All Her Fault" — is Irish, and she sets all of her books in Ireland; "All Her Fault" is specifically set near Dublin, the country's capital. The series, though, brings the action to an affluent Chicago suburb, showing off some of the Illinois city's sights like its iconic skyscrapers and the Bean statue in Millennial Park during interstitials and before scenes that take place in the city proper (Jenny, who works in publishing, spends quite a lot of time in Chicago during the show's narrative). This doesn't affect the story at all, and frankly, the story works outside of Chicago, giving the characters room to play within the city and near the luxurious suburban homes owned by the Irvines and Kaminsky.

Obviously, there are police officers in the novel version of "All Her Fault," but they pretty much only float on the periphery and aren't a direct part of the action. This changes in the TV adaptation, in which we get a really big focus on Michael Peña's detective Jim Alcaras, who ends up investigating Milo's case and working closely with Marissa and Peter.

As we delve into Jim's personal life, we learn that he has a special needs son who is unable to speak and needs incredibly particular care to help him thrive. The care center he attends when we first meet Jim is chaotic and feels really overwhelming for Sam (Orlando Ivanovic), and the school Jim hopes that Sam can attend is expensive, requiring financial aid. When Jim arrests a young man who had Xanax on his person at the time of that arrest, he eventually fudges the results — pretending the pills were just Tylenol and not a controlled substance — because the boy's father might help Sam get into the better school.

Frankly, it's a little odd and extremely interesting that Jim's gambit never comes to light, but this does provide a much better situation for Sam. All in all, Jim is a great addition to the series, and it helps that we understand the conflicted internal life of the detective investigating Milo's disappearance.

Unfortunately, some of Jenny Kaminsky's internal life is diminished thanks to the focus on Jim, as well as Peter's siblings Brian (Daniel Monks) and Lia ("The Bear" favorite Abby Elliott). In Andrea Mara's novel, Jenny is having marital issues with her husband Richie, all of which are constantly exacerbated by her judgmental and even cruel mother-in-law Adeline, who makes a habit of stopping by the Kaminsky household and criticizing Jenny for being a working mother. Add in Richie's suspicion that Jenny might be having an affair with a work colleague, and you've got a bad situation.

There is no work colleague who may or may not be trying to romance Jenny in the TV version of "All Her Fault," and there's also no Adeline. What the show does instead is make one thing quite clear: Richie, played by Thomas Cocquerel, is trying to balance his own career with Jenny's and often makes professional and personal sacrifices in order to be a good dad to Jacob. Still, he falls short often — in the pilot, he drags Jenny away from an important work meeting because he doesn't know how to put his own kid to bed — though eventually, Richie and Jenny both vow to work harder at both their relationship and parenting Jacob.

Okay, now let's talk about the ending. The gist is the same: we find out that Jacob's nanny, a woman known as Carrie Finch who was originally named Josephine Murphy — played by Sophia Lillis, whom you might recognize from "Dungeons & Dragons: Honor Among Thieves" — kidnapped Milo, because Milo is actually her son. Years prior, the woman once known as Josephine got into a car accident with her newborn baby, and when she woke up, she was told that her son had died in the crash. As it turns out, Peter, Marissa, and their newborn baby were on the other end of that fatal car accident, and while Marissa and Carrie were both unconscious, Peter picked up Carrie's baby and didn't correct police when they assumed it was his son Milo. In reality, Peter and Marissa's son Milo died in the crash, but Peter simply steals the baby and claims it was Milo the entire time. Marissa isn't Milo's biological mother; Carrie is, and she figures that out when she realizes that both she and Milo have synesthesia, which is genetic. (Synesthesia refers to a neurological phenomenon where you experience sensations using different senses; words might take on colors or tastes, for example.)

Carrie heads to the Irvine house to confront Peter, and in the process, she accidentally shoots Marissa's best friend — and Lia's boyfriend — Colin (Jay Ellis), who ultimately dies. Peter then shoots and kills Carrie and tells Marissa that they have to claim self-defense so that Milo isn't taken away from them. Marissa has other ideas. After knowingly eating soy products at Colin's memoral service, Marissa kisses Peter, who is deathly allergic to soy ... thereby killing him for his crimes against both her and Carrie.

"All Her Fault" is streaming on Peacock now.