Just because All Her Fault is based on a novel by Andrea Mara doesn't mean the TV adaptation didn't go through some book-to-screen changes. The Peacock series, which premiered Thursday, November 6, follows a mother named Marissa (Sarah Snook) whose son, Milo, disappears from his first playdate. The search for Marissa's child uncovers secrets about those closest to her, with everyone becoming a suspect in the kidnapping. While All Her Fault has largely stuck to its source material, the biggest differences came from expanding on characters including Abby Elliott's Lia and Daniel Monks' Brian. "Both our characters - out of the main cast - probably diverged the most from Andrea Mara's novel. [Creator] Megan Gallagher not only fleshed out our characters, but also my character isn't written as being disabled in the novel," Monks, 34, who has hemiplegia, exclusively told Us Weekly. "But Megan wrote him as having a physical disability - partly also because she is the parent of a disabled child and she felt very passionate about providing interesting and also progressive disabled representation within the story." 'One Day' and More TV Shows Based on Popular Books Monks was grateful for the chance to tell an enriching story through Brian. "For me with the novel, I started reading, and their Brian seemed unrecognizable from the one that Megan had written," he noted. "So, I was like, 'I think that needs to wait for later so I can focus on the scripts.'" Elliott, 38, had a similar experience, sharing with Us, "With Lia, it was the same kind of thing when I talked to Megan at the beginning of the whole process. She explained the story and she said, 'Don't read the book until after because you don't want that in your head.'" She continued: "Lia came in much, much later, and she's a New Yorker. So it's a very different vibe, and Megan had fleshed out these characters so much already that they were completely different than the book." Sarah Enticknap/PEACOCK In Peacock's version of All Her Fault, Lia is "a recovering pill addict, a younger sister and a loose cannon." "I just thought about the people that I've encountered in my life that have gone through recovery and addiction," Elliott told Us. "Also, [I thought about] the younger sisters that I know. It was just trying to make their voice known." Monks, meanwhile, built out his own version of Brian. "I only had the first three episodes, so not only do I not know the ending or the twists and turns, but I also don't know my backstory. As soon as I was cast, I had a Zoom with our creator to make sure that the disability was tailored to my specific physical disability. But in doing so, she also revealed a lot about my character's backstory and the disabled narrative that she wanted to explore within this story," he recalled. "Those conversations and then getting the latest scripts was the most helpful thing." Fall 2025 TV Schedule: See When Your Favorite Shows Will Air Through Brian, Monks was able to show more of his own story, adding, "That was the most thrilling and compelling thing. You never want representation to feel like a PSA. So to have it so expertly woven within this gripping and thrilling roller-coaster ride of a story in a way that you might not even necessarily clock the representation you're experiencing. That's the kind of ideal when it comes to furthering minority representations.." All Her Fault spent eight episodes built up to the reveal of who kidnapped Milo. According to Monks and Elliott, there were points during filming that they were just as in the dark as viewers will be. "I didn't really know right out of the gate if my character was involved or not. It is a whodunit, so I just tried to play things as honestly as possible. I really go back to what the essence of the character of Lia is, and she is just really trying to make her voice known and she's extremely impulsive," Elliott teased. "Also, the knowledge of what Megan had already written, it led to playing different levels on that and doing multiple takes." She concluded: "I come from comedy, so I'm not used to having the luxury of doing take after take and really finding things. So, to be able to do that was such a gift." All Her Fault is streaming on Peacock.