In the eighth episode of All Her Fault's first season, Carrie finds herself in control of the Irvines' mansion, holding Colin and the rest hostage. Colin, filled with bravado, attempts to be the hero and ends up getting shot in the abdomen. Carrie grants Lia the chance to call for an ambulance and wait at the gate while allowing Brian to head upstairs and keep watch over Milo. Unfortunately, Colin's wound proves fatal, and he bleeds out on the floor.
As for the reason behind Carrie's kidnapping of Milo, it is revealed that he is her biological son. Six years ago, during an accident on their way home from the hospital, the Irvines were involved along with Carrie, whose real name is Josephine Murphy. Both Noah and Milo were born on the same day. Following the crash, Peter was the first to regain consciousness. He turned back to see that Marissa and their son were gravely injured. The real Milo was dead, and Peter decided to switch him with Carrie's baby.
Carrie heard her baby crying, but she was told by all that she was hallucinating. No one ever believed her.
After Colin's death, Carrie begs Marissa to protect Milo from Peter. She is about to show Marissa some evidence on her phone when Peter moves towards her. Carrie falls back, trying to get free from Peter, but he grabs the gun and a struggle ensues, even though Carrie basically lets him have the gun. Peter turns the gun on Carrie and shoots her, acting like it is self-defence but Marissa knows it was an execution. She demands the truth and threatens to tell the police about the baby swap.
Trapped, Peter finally admits to the switch he carried out six years ago. He makes Marissa promise to hide the truth so that they don't lose Milo. The police soon arrive, and Marissa quickly grabs Carrie's phone and hides it in her pocket. Later, Peter tells the police that he acted in self-defence, and Marissa backs him up. She checks Carrie's phone and finds a voice recording of Peter killing Carrie's dad in the motel.
Rob was slated to rendezvous with Peter and secure the ransom money, but his ill-advised threat to expose Milo's true lineage to the press proved to be his undoing. Peter, emboldened by his newfound control, dispatched Rob and, in a bid to cover his tracks, covered Milo's face before driving him towards the police station.
As Peter stalked Marissa, he demanded Carrie's phone, intent on erasing any evidence that might implicate him. Marissa's horror grew with each revelation, as she realized the depths Peter would sink to in his quest for Milo. Silently, she surrendered the phone, promising to keep the truth a secret alongside him.
The police concluded that Carrie's death was a result of self-defence, but Marissa found herself increasingly trapped. She fretted over her inability to divorce Peter and claim Milo, fearing the consequences that awaited her. Moreover, she knew the police would take Milo from her if she reported the truth. In a desperate bid for support, she confided in Jenny, who reminded her that Milo was her son and that she must not let anyone take him away.
Meanwhile, Lia focused on hosting Colin's wake, with Marissa by her side, ensuring everything was in order, including the catering. But on the day of the wake, Marissa took a calculated risk, ingesting soy—which Peter was deathly allergic to—and then passionately kissed him, triggering an allergic reaction.
As it turned out, she had also surreptitiously placed an expired EpiPen in his jacket and conveniently 'forgot' the emergency EpiPen in the car. As Lia called for an ambulance that would arrive in eight minutes, they all watched in horror as Peter's life slipped away while waiting for help.
In a parallel turn of events, Alcaras uncovered the truth about Milo during a school registration process for Sam. One of the questions inquired about synaesthesia, a detail that shed light on Milo's unusual abilities and the web of lies that had been woven around him.
The finger of blame for Peter's demise is ever-present, yet shrouded in uncertainty. As Alcaras pieced together the fragments of the tragic event, he learned of a genetic neurodivergent condition that played a pivotal role. Speaking with the paramedic who arrived at the scene of the accident, he discovered that Peter was the sole conscious being amidst the chaos. As he exited the hospital, Greco's call brought a heavy heart to Alcaras—Peter had passed away.
The police's next move was to bring in Lia, hoping to prove Marissa's intention to take Peter's life. But Lia stood by Marissa's side, her heart still raw from Peter's final words, which seemed to pin the blame for Colin's death squarely on her. It was almost as if he wanted to provoke her into a relapse. In the end, with no concrete evidence, Peter's death was ruled a tragic accident.
As the story unfolds, Marissa relocates to a house opposite Jenny's, where they spend their evenings watching over the boys and sipping wine while exchanging friendly conversations. Alcaras introduces Sam to his new school and finds peace in what he had to do to get him there. He also pays a visit to Marissa, sharing his findings and assuring her that the case is closed. With a sense of justice served, he finds it easier than expected to let go of the case.
He shares Milo's condition with Marissa and asks her to keep an eye on it. Marissa is left stunned and grateful for Alcaras' understanding of her decisions. The show ends with Marissa and Jenny watching the kids play in the background as they savor their wine, their bond strengthened by shared experiences and a sense of camaraderie in the face of adversity.
