8 Differences Between the ‘All Her Fault’ TV Series and Book

Warning: All Her Fault spoilers ahead!

All Her Fault is full of twists and turns that even fans of the book couldn’t have seen coming.

Released on Peacock in November 2025, the crime drama stars Sarah Snook as Marissa Irvine and Dakota Fanning as Jenny Kaminski, two affluent working mothers whose lives unravel after Marissa’s son vanishes from a playdate, and Jenny’s nanny, Carrie Finch (Sophia Lillis), becomes the prime suspect.

Though the TV series differs in many ways from the book it was based on — written in 2021 by Irish author Andrea Mara — the premise and major plotline remain the same. Showrunner Megan Gallagher told TheWrap that she “would never in 100 million years” change the book’s “whooper” ending in which Carrie reveals that Marissa’s husband, Peter (Jake Lacey), secretly switched their newborns after a car accident killed his own child six years earlier.

“What you’re doing with an adaptation … is not so much changing material as adding to,” she said in the November 2025 interview. “Just because of the format of television, especially when you’re looking at eight big, chunky episodes, you need so much material, often more than almost any book would give you.”

Gallagher likened a TV adaptation to an accordion that she stretched with “great tent poles” that Andrea provided. “What can I add to it, to build to those twists and supplement those twists and make them as strong as possible?” she explained. “It’s not about changing the fundamentals. It’s about adding to what she’s given me.”

So, where exactly did Gallagher add on to Mara’s original story? Here are all the biggest differences between the All Her Fault series and the book it was based on.

The book doesn’t take place in Chicago

Though Mara’s book takes place in Dublin, Gallagher shifted the story and all its drama to Chicago. She said the transition came easily, noting that the series’s central themes of guilt and pressure on working mothers translate anywhere.

“This is very universally understood kind of thing,” the showrunner told the Associated Press in November 2025, noting that it’s something she’s experienced. “I had years and years and years of just trying to do it all, and I nearly hospitalized myself with exhaustion. So these themes are very, very present in me and in my life. It was painful to dive into at times, but I’m glad I did it.”

Lia isn’t a major character

Abby Elliott’s portrayal of Peter’s sister Lia was far more central to the plot in the TV series. However, on the page, her character lived in New York and only appeared towards the end of the story for moral support.

Her secret relationship with Marissa’s colleague Colin (Jay Ellis) is still present in Mara’s novel, but not nearly as serious. Rather than being in love, they merely went on one date a long time ago.

Brian isn’t disabled 

In the All Her Fault book, Peter’s brother Brian (Daniel Monks) is able-bodied, but in the series, he suffered an injury as a child that made it difficult for him to walk without a wheelchair or crutch. His disability is a major plotline in the show as viewers learn that Peter has allowed Lia to believe she was responsible for his accident when he was the one who actually caused it.

“I really wanted to get a disability story line on the screen that would be meaningful to the disabled community,” Gallagher told TheWrap, noting that the on-screen plot for characters with disabilities often involves perseverance.

“As it was explained to me, it’s quite offensive,” she said. “So being able to put a story line on the screen that was about saying, ‘Yeah, I’m disabled, and this is what I need’ and get over it is so much more powerful.”

Detective Alcaras is a woman 

Michael Peña may play Detective Alcaras in the All Her Fault TV series, but the character is a woman named Detective McConville in the novel. Gallagher also dove more into the investigator’s role as a parent of a child with a disability and the lengths he was willing to go to give him a better life, telling TheWrap that Detective Alcaras’ gray morals mirrored Marissa’s.

“What Marissa is grappling with in Episode 8 is the difference between law and justice, and that’s also what Michael Pena’s character is grappling with, is law and justice — they’re often not the same thing,” she told TheWrap. “Both of these characters care about right and wrong and morality and ethics … But sometimes the what feels right isn’t strictly legal.”

The showrunner also said that much of Detective Alcaras’ story line with his son came from her own life, as she has a child who has autism. “Michael did a really, really great job of encapsulating the feeling of isolation,” Gallagher told Vanity Fair in October 2025. “You are on a lonely island. It might be an island full of tons and tons and tons of love, but it is a little lonely.”

Jenny doesn’t get divorced

Though not as prominent as Marissa and Peter’s relationship, viewers do get a peek into Jenny’s marriage to her husband, Richie (Thomas Cocquerel). After years of built-up resentment, she asks for a divorce, citing his lack of initiative when it comes to taking care of their son.

The book actually focuses more on Richie and Jenny, including an entire subplot about him receiving a letter insinuating that she had an affair. Eventually, the mysterious sender is revealed to be Richie’s mom, Adeline, who isn’t even mentioned in the series. And unlike Fanning’s character, Jenny seems more open to reconciling with her husband in the book.

Peter doesn’t shoot Carrie

The same people die in the All Her Fault book and TV series. However, the order and manner in which they die are a little different.

For starters, Peter doesn’t kill Carrie in their home with the gun she had first pulled on him. Mara’s version had the father smothering the nanny with a pillow in her own home. Gallagher told TheWrap that the tweak of how Peter chose to kill Carrie before she could reveal more to Marissa about what he had done said “a whole heck of a lot about Peter and how desperate he is in that moment, and what he’s capable of.”

“What other ending, if you think about it, is there for poor Carrie?” the creator explained. “I don’t know what we would do beyond that.”

Carrie doesn’t kill Colin 

In the series, Colin tragically dies during Carrie’s confrontation with the family when she unintentionally shoots him. The All Her Fault book, however, sees him killed by her father, Rob, instead.

After killing Carrie, Peter is worried that Rob (played by Eroll Shand in the series) will want to avenge his daughter’s death instead of accepting the ransom money for his kidnapped son. So he asks Colin to go in his place.

Colin obliges, and Rob ends up killing him, thinking he was Peter. Then Peter shows up and kills Rob in the same manner that plays out in the series.

Peter is allergic to shellfish, not soy

Peter’s deadly allergy to soy plays a major role in how he dies in the series. Though Marissa still kills her husband at the end of All Her Fault, she uses a different allergy to do it in the book: shellfish.

Being hyper-aware of her partner’s allergies, Marissa kills Peter in the novel by making sure he eats shellfish while they’re on vacation in Spain. Though Jenny is clearly in on the plan in the show, it’s not clear if Marissa disclosed her intentions in the book.