Breaking Down the Devastating Ending of All Her Fault

Warning: This post contains spoilers for All Her Fault

Years of buried lies have unraveled by the time Carrie Finch (Sophia Lillis) shakily raises a gun at the Irvine family in the finale of All Her Fault. Across eight episodes, the series explores how love can twist into possession and how far a parent will go to protect their child. The ending doesn’t simply answer what happened to Milo Irvine (Duke McCloud) after his mother Marissa Irvine (Sarah Snook) arrives to pick him up from a playdate only to learn he has disappeared; it exposes the crime that made his abduction feel inevitable, then asks what justice looks like when the person you must escape is the one who shares your bed.

The Peacock limited series follows how Milo’s disappearance affects the Irvines, an affluent Chicago family, as Marissa (Sarah Snook) searches desperately for her son. Based on Andrea Mara’s novel, the series begins as a domestic thriller and deepens into a study of truth, control, and the lengths parents will go to protect the worlds they’ve built.

“It just feels so immediate,” says executive producer Nigel Marchant. “You’re completely thrown in with this premise—it’s any parent’s worst nightmare.” 

The night that breaks everything open

The series opens on a quiet Chicago afternoon when Marissa goes to pick up Milo from the home of Jenny Kaminski (Dakota Fanning) and he isn’t there. Jenny insists she never arranged the visit. Panic spreads. What begins as a missing-child case becomes a much darker story about what happens when love itself turns dangerous.

Over the following episodes, police discover that Carrie Finch, the nanny Jenny hired, picked up Milo from school. Surveillance footage soon surfaces showing a man arguing with Carrie—Kyle Smith (Dominic Masterson), Carrie’s ex-boyfriend—at the Chicago Marathon, revealing she wasn’t working alone. With Kyle’s identity on the verge of being discovered, Carrie takes Milo to her father Rob’s (Erroll Shand) motel room, hoping to keep him hidden and safe. 

When Carrie finally appears in the Irvines’ living room with a gun, she shares her real identity: Josephine Murphy, the woman involved in a car accident with Peter (Jake Lacy) and Marissa six years earlier. Marissa is stunned but Peter isn’t. What Marissa doesn’t yet understand is why Josephine took their son.

The finale’s big reveal

In the Irvine family’s home, lamplight settles over a night on edge. Josephine stands with trembling hands, the weapon raised at people who, moments earlier, were locked in quiet conflict. Marissa and her husband Peter Irvine (Jake Lacy) widen their eyes in shock. Then Colin (Jay Ellis) lunges. The shot splits the air. He falls, blood blooming across his shirt. “Call an ambulance,” Josephine urges. Colin dies before help arrives. “I never wanted to hurt anyone,” she sobs. 

When Marissa asks who she really is, Josephine gives her true name.“No, you’re dead,” Marissa says. “I wanted to be,” Josephine replies, her voice scraped raw. She didn’t come to take Milo back, she explains, but for a promise—mother to mother—that Marissa will protect him. Protect him from whom? “Him,” she says, staring at Peter. “You don’t know what he’s capable of.”

Then, Peter lunges. The gun fires. Josephine falls. Minutes later, with her body on the floor, Peter tells Marissa what happened, a confession that unspools in shocking fragments: a night drive six years ago, an intersection, two cars colliding. Marissa was unconscious. Their infant son died on impact. Across the wreckage he heard crying—Josephine’s baby, alive and terrified. He grabbed the child, replaced their dead infant in Josephine’s car seat, and drove home with her living one.

“He wasn’t ours,” Marissa says, the words hitting hard as gravel. “He was hers.” Peter tries to justify it—he thought Josephine was dead, the baby needed someone—but his reasons keep shifting.

For Marchant, that self-justification is central to Peter’s downfall. “There’s an element where you almost understand his actions until they go so far beyond what any sane person would do,” he says. “There’s always that justification: he feels he’s protecting his family, looking after them, needing them. But it’s all manipulation, and he never sees it that way.” 

Gallagher had a single goal from the start: to build characters layered enough that their worst choices still felt understandable. “From the pilot episode, that was my north star,” she says, referring to the finale’s devastating twist. “I wanted to build all of those characters up so that when all that happens and explodes in that Irvine living room, it just landed.”

As Marissa absorbs the truth—that she married a monster—the horror isn’t loud so much as paralyzing. For Snook, who plays the scene with quiet devastation, it meant portraying a woman forced to solve an impossible equation: between a husband who doesn’t play by society’s rules and a son too young to protect himself. “There were big decisions to be made,” Snook says. “For me, a big thing was, how does Marissa hope this is going to be beyond the end of our story? For Milo, what’s his future?”

What happened to Milo?

After picking Milo up from school, Josephine hid him at an apartment rental, then moved him to a motel with her father Rob when authorities discovered an image of Kyle from the Chicago Marathon’s surveillance footage. While Josephine ran out to buy a cake for Milo’s birthday, Peter arrived with a duffel bag of cash in exchange for the boy’s safe return. 

As Rob counted the money, his back turned, Peter grabbed a lamp and struck him, killing him instantly. He found Milo hiding in the closet, placed him in the trunk of a car, and abandoned him outside the police station, making it look like the kidnappers had brought him back. By the time Josephine set foot in the Irvines’ living room, Milo was already home.  

The unresolved questions

When the police arrive at the Irvines’, Detective Alcaras (Michael Peña) briefs the Irvines: Jenny’s nanny “Carrie Finch” is actually Josephine, and the body at the motel belonged to Rob. Peter offers a version of events that bends the truth: Josephine’s baby died in the crash, the gun went off during a struggle, she must have been “mentally unwell.” When Alcaras asks Marissa what she thinks, she reluctantly echoes Peter: “I think she was just crazy.”

Later, Marissa plays an audio file found on Rob’s phone—the one Josephine meant to give her. The recording captures the motel encounter where Rob died. Peter visited while Milo hid in the closet. Rob counted ransom money, his back turned. Peter grabbed a lamp. The impact landed, swift and final. “I saved him. He was mine. He was my son,” Peter said. Another piece clicks into place to Marissa: Peter? put Milo in a trunk and abandoned him at the police station, staging the boy’s “return” to close the circle of his lie.

Marissa climbs the stairs, but Peter follows. “We were never going to be safe,” he explains of killing Rob. He asks for Rob’s phone. She hesitates, then hands it over. He walks away, leaving her on the landing, sinking to her knees in tears.  

It’s a devastating exchange where fear and denial finally give way to reality. Gallagher says she tried to build out Peter and Marissa’s moral complexity from the start. “I’ve never once written somebody who’s just evil, like sociopathically evil,” she says. “There’s not much to sink your teeth into. I much prefer working with characters who have made terrible decisions, but I could put myself in their shoes, and be like, maybe on a bad day, I might see at least where they’re coming from. Because everybody’s the hero of their own story.”

The next morning, Peter’s mask slips. He snaps at Milo over scissors, grabbing him hard. “Do not run away from me,” he says, voice rising. “You are not allowed to run away from me… You are mine.” Marissa watches, seeing at last the true depth of his need for control; she confides in Jenny later but fears turning in Peter will mean losing Milo.

Alcaras, meanwhile, keeps tugging at loose threads. Josephine’s former guidance counselor recalls that words, tastes, and colors would sometimes get mixed up in her head—episodes that left her distressed and that the counselor never understood. The memory lingers. Later, Alcaras consults a specialist who explains synesthesia, a rare hereditary condition where the senses cross. Milo’s drawings, those unusual color choices that once seemed like the result of a vivid imagination, now look less like creativity and more like inheritance.

At Colin’s wake, among bottles aging in the dark, Marissa kisses Peter. “I just missed you,” she explains. His face changes. He’s allergic to soy, something she has always managed with careful precision. Panic floods his eyes. He races upstairs, jabs an EpiPen into his thigh—three years expired. Marissa calls for Lia to dial 911, asks for the emergency kit from the car.

Lia (Abby Elliott) can’t find it. Eight minutes until help arrives. Peter’s throat tightens. Marissa’s expression hardens. “It’s true. I manage your allergies for you,” she says softly, meant only for him. Peter’s eyes widen in understanding. She ate soy deliberately, kissed him knowing what it would trigger. A flashback confirms she removed the kit hours earlier. Peter dies. “It’s definitely a moment of justice,” Snook says. “It’s a moment of sadness. It’s very complex—difficult one to play—because in this moment I’m taking away my son’s father and I want my son to have the memory of a father who was good.” 

What Marissa does doesn’t come from hate. It comes from love pushed past the breaking point—the kind that protects by destroying and saves one life by ending another. Snook calls the story “tragic in that Greek tragedy kind of way,” a description that fits the finale’s moral gravity. Like the great tragic heroines, Marissa isn’t driven by vengeance but by inevitability, by the realization that the love that once sustained her family has also doomed it. Her act is both punishment and release.

The detective who sees everything

At the precinct, Alcaras and his partner review Peter’s death. The partner suspects Marissa. Alcaras shrugs. “We might never know,” he says. Later, they question Lia about the food labels at the wake: did Marissa read them to see whether the dishes contained soy? She pauses, remembering Peter blaming her for Colin’s death. She makes her choice, covering for her sister-in-law. “She’s not forgetful,” Lia says carefully. “But she’s human.” Peter can’t hurt anyone else now—not from the grave.

When Alcaras visits Marissa at home later, he explains synesthesia: how it’s inherited, how Josephine had it, how Milo has it, too. “The only person awake was your husband,” he says of the car accident six years ago. “Whatever decisions he made in that moment you weren’t a part of.” Alcaras guesses it was Peter who killed Rob and hid Milo, that Marissa had no idea until Josephine appeared with a gun. “I know you were stuck, Mrs. Irvine. You couldn’t tell anyone the truth, so you made some choices.” While the case is closed now, he says he feels “fine” about the way things were resolved—he’s accepted that Marissa won’t be held accountable for killing Peter. 

Snook calls Alcaras’s decision to let Marissa go a moment of recognition without judgment. “It’s a moment of complicity,” she says. “Alcaras is saying, ‘I see you, I see what you’ve done, and I’m willing to overlook those crimes, because of the horror that has come before. Now, it’s better for Milo to have a stable, solid life with a parent, and you are the closest thing he has to a parent.’”

From the beginning, Gallagher knew Alcaras, who isn’t in the novel, and his final scene would define the show’s conscience. “For a character like him, who’s a good guy and sees himself as a good guy who does the right things, for the first time, he’s really kind of stepping over the line into a slightly more gray territory,” Gallagher says. “I think it would be hard for him to speak the words out loud, so silence worked a little bit better. But we as an audience fill in the gaps.”

What follows is less a resolution than a reckoning—a reminder that in this world, justice may depend on who’s willing to look away. “Right and wrong and the law aren’t always the same thing,” Gallagher says. “I’m not advocating that everyone goes out and break the law, but life is often more complex than the legal system strictly allows for.”

A house still standing

Later, Marissa and Milo arrive at Jenny’s (Dakota Fanning). The boys blow bubbles in the yard, light catching the soap as it drifts, while the women sip wine on the porch, their backs to the camera. Everything looks ordinary again, but ordinary life now carries a different weight.

Through Marissa’s impossible choice, All Her Fault reaches what it was circling all along: the peril and purity of parental love. It’s love as both salvation and surrender, a force that can nurture or destroy depending on who holds it. The finale offers no resolution, only recognition—that the instinct to protect can blur into possession, that justice can take many forms, and that sometimes the hardest act of love may be the one that leaves blood on your hands.

Marchant hopes the ending lands on several levels. “I’d love for an audience to come away incredibly satisfied with the thriller part of it but also thinking about those inequalities: how we hold women to a harder account than men,” he says. Gallagher hopes the series also underscores the quiet toll of being a working mom who is the “CEO at work and the CEO of the household.” “Women my age are stretched so unbelievably thin that it’s reached a climactic point,” she says. “This has been touched upon in TV and films, but I don’t think it’s been dug into as much as it should have.”