Kate wakes up and finds an envelope from Gemma at her door. Inside is a tie belonging to Simon with a note: "He left it at my place." Kate confronts Simon about it, and he suggests that Gemma likely just wants to cause trouble for them, possibly having stolen a tie from their party or his office. He then leaves for work, but Kate can't stop thinking about it. Kate checks Gemma's present box and tears up looking at it. Later, she goes to her parents' house to drop off Amelie and asks her mom if she knows Gemma is gone. Her mom notices she doesn't look happy. Kate goes to her lecture, and after school, a classmate invites her to a night out, but she declines, saying she’s a mom now. While walking, Kate's friend spots Carly and stops her; they are friends as well. Kate and Carly look awkward around each other. Carly starts to leave, but Kate stops her and accuses Carly of stalking her for Gemma. Carly insists it isn't the case this time. Kate mentions the note Gemma left, implying Simon slept with her. Carly advises Kate to confront Simon because "once a cheater, always a cheater." This suggestion sticks in Kate's mind, and she goes to Simon's office. She asks Simon to go out to order lunch for them from the café, using the time to snoop through his phone, where she finds a picture of a drunk Gemma. Simon returns and mentions Gemma again, which annoys Kate. He brings up the issue with Tom, suggesting they let Tom stay with them when things get better, but Kate strongly opposes this idea. After the waiter brings in their lunch, Kate asks Simon why Gemma waited so long to expose their affair two years ago. Simon thinks it's because Gemma wanted to understand the extent of his relationship with Kate. But Kate doesn’t have the patience and confronts Simon about the picture of Gemma on his phone. Simon claims it was meant to shame Gemma for how miserable she looks. Kate is more concerned that Simon is so focused on Gemma and even uses insulting language to describe his ex-wife. After leaving the office, Kate runs into Sian, who starts talking to her as a friend of Simon's. Sian mentions Gemma's departure is just as Simon predicted, confirming Kate's suspicion that Simon keeps many secrets from her. Sian also shows Kate a post about Gemma's house being for sale, and Kate decides to go there, pretending to be a buyer. Sneaking around Gemma's bedroom, Kate finds a sticky note with what seems to be Gemma's new address. Just then, Anna enters the house, speaking with the real estate agent downstair about arranging the remaining items. Kate tries to sneak out but is spotted by Anna, who confronts her about her presence. Anna spills immediately she heard Gemma and Simon getting intimate the other night and has no reason to lie for Gemma. Kate insists she doesn't believe any of it and swears to confront Gemma to stop her from bothering them, using the address she just discovered. Anna acts surprised Kate knows the address, while she was the one who placed notes around the house with this address and that the estate agent was part of their plan. Kate goes to a hotel and asks for Gemma Foster, but the name isn't listed. When Kate calls Gemma, she hears her phone ring in the lobby and sees Gemma standing in a corner. Kate walks over and is surprised to find Gemma with Kate's baby, Amelie.

A flashback shows Susie, Kate's mom, waking up by her husband, Chris. They are getting ready to look after Amelie when Susie gets a text from Gemma asking to meet secretly. Susie actually goes, surprising Gemma. Gemma asks about Kate's childhood dreams. Susie says Kate wanted to travel the world but things changed when she became a mom. Gemma tells Susie about her and Simon, telling Susie to help her daughter with this information. In the office, Mark, Kate's godfather, notices that Kate is upset this morning and goes to ask Simon, but he says everything is fine. Gemma calls Simon and warns him that things are about to go wrong for him, and if he doesn’t pack up and leave, she will destroy everything. He chuckles, dismisses her, and she hangs up. Back in the hotel lobby, not only was Amelie there with Gemma, but also Susie and Chris. Kate's parents try to talk to her about Simon, but Kate defends Simon, calling Gemma mental. But Gemma has already done her research and knows that the fancy house was bought by Chris and Susie. It is in Kate’s name alone because they don’t trust Simon. His business is in the name of Kate’s godfather because nobody trusts Simon. And Kate is here because she doesn’t trust him either. At this point, Kate lies and says she already knows about what Simon did and they have already worked through it because they have a real marriage and nothing needs to change. She then demands Gemma to leave her and her family alone. Gemma returns to her room and sees Tom relaxing there, waiting for his mom to sort everything out. Gemma tells him that things didn’t go as planned and they really have to leave town. Kate confronts Simon at home, and when he lies again, as he always does she warns him to be honest now or else he'll have to face all the consequences. Simon doesn’t become a better person, but this time, Kate is a wife with more power over him. She has wealthy parents who bought their house, and her godfather is Simon's sponsor. For once, Simon admits what he did. However, he still claims it was just physical and he has no feelings at all for Gemma. He says Gemma is way less attractive, kind, and loving compared to Kate, and what he did was just out of politeness. It sounds ridiculous, but it's something Kate wants to hear because she has always been competitive with Gemma. However, Simon still seems obsessed with Gemma, and this makes anger her. In the hotel, Gemma finds Tom crying in the bathtub and comes in to take care of him. Meanwhile, Kate tries to play the "cool girl" monologue in her mind because her competition with Gemma gets the better of her. She tells Simon that she won't become the bitter woman who got cheated on, like Gemma, and that they have to work through it. But at night, she still can't sleep, so she texts Gemma and asks to meet at the hotel again. Kate mentions that Gemma said Simon hadn't thrown everything away from their marriage and asks her what those things were. Gemma says there are many, like the watch she gave him that he still wears, and the cufflinks he wore on their wedding day, which were a 7th-anniversary gift from her. Also, the furniture and other items are all over Kate's house, and that Simon said he dreamt about Gemma.

Kate is in denial because she can't stand this harsh truth. suddenly, Gemma takes out her phone, takes a picture of Kate, and tells Kate to follow her home. There, she looks through all of her albums while asking Kate about the wedding's food choices, how Simon is in bed with Kate, and tells her how that always reflects on what he had with Gemma before. Gemma then shows Kate a picture of a younger Gemma and puts it next to the one she took earlier of Kate, and they look very similar. The gift to Kate was Simon's wedding vow to Gemma, stating that he would be obsessed with her forever. Now, Kate sees it clearly: Simon wants her because he sees a younger and more exciting Gemma in her, and that's it. Gemma tells Kate to escape this before she wastes 15 years of her life and ruins her daughter as well. The next morning, Simon shows up at Gemma's house and bangs on the door, but no one answers. Later, he struggles even more when his card balance is insufficient and, for some reason, his partner Mark isn't in the office and is unreachable. Kate texts him to come home now, and he arrives home to find a moving truck in front of the door. Chris goes out and has a quick talk with Simon about their previous agreement, stating that if Simon upsets Chris's daughter, he's out the door. They all now know that Simon has ruined everything within just two years of marriage with Kate. Mark happens to be there as well and confiscates Simon's car, including his laptop bag inside. he throws out a duffle bag, which is all the belongings Simon has. Kate comes out of the house and tells Simon he will never see her and Amelie again, and her dad has already hired a very good lawyer to make sure it happens. She and her daughter will now move to France. Simon is in tears, trying to open the door of the house, but they have already changed the lock. Just when he is about to have a mental breakdown, Gemma pulls up, and he lashes out at her, hitting the window and leaving his breath and spit all over the glass. But Gemma doesn't show any emotion; she just drives away and calls Tom, saying they can go home now. However, Tom is concerned about his dad, and Gemma has to reconsider. At the end of the day, no matter how horrible Simon is, he is still the father of her son. Gemma drives back and tells Simon that she will put him in a hotel for a few days on the outskirts of town to sort things out himself, and he can leave without upsetting Tom. Simon, once again, has a chance to manipulate Gemma and blame everything, including his own mistakes, on her. Simon then snatches Gemma's phone, finds out Tom's address, grabs his duffle bag, and goes there on foot to have a talk with Tom about how bad his mom is. For a moment, Gemma contemplates running him over, but she knows she's better than that and instead just drives off. Of course, she arrives at the hotel first and tells Tom to pack up their things to leave. Simon finally makes it just when Gemma drives off with Tom in the car. They soon return to the house and see a new family has already moved into Anna's old house. Tom is shocked to see that all their old furniture is gone, thanks to Anna.

Gemma tries to cheer Tom up with the idea of a fresh start for them, which they can start by redecorating this empty house. All of this and Tom to tell her he's thinking about moving out next year. Gemma is stunned and asks Tom again what Simon said to him because it clearly made a big impact but he still doesn’t want to say. Later, Simon arrives at the house and waits for Tom outside. Tom comes out and confronts him. Simon starts to trash talk about Gemma again. But Tom calls simon out for using him to get at Gemma. Fed up, Tom walks away, and Gemma stops Simon from following him inside the house. Simon says he should stab Gemma in the face and she says maybe he should do that to himself instead before going back to the house as well. A few minutes later, the doorbell rings, and Gemma opens the door with a shear in her hand, but it's just the new neighbor coming over to say hi with her two little kids. Gemma has a flashback of her once happy married life before everything went sour. At night, she goes out with James, Tom, Ros, and her husband. James asks about Tom's situation, and Ros suggests they all should look after each other from now on. Just then, Simon appears at the window of the restaurant and starts knocking on the door. Gemma tells everyone she'll deal with him herself and goes out. Simon becomes so desperate he even proposes they come back together for the sake of Tom. Gemma begs him to leave them alone and even offers him money. Simon goes on about how it's normal to be toxic because that's how family is until Tom comes out and tells him straight to his face that he's just a liar who keeps lying to himself that he isn't a failure. Later, Gemma and Tom come back home with James. Gemma finds a piece of paper at the door and picks it up. James brings Gemma a present, a pair of earrings. Gemma is grateful but excuses herself to go get some water in the kitchen. Tom asks Gemma about her parents, who died in a car accident and were very loving toward her. Tom comments that she is luckier than he is because Simon never stops bothering him. Tom thinks Gemma's actions were meant to punish Simon, but Gemma says Simon starts everything first, and she only protects herself.

Tom returns to his room, and Gemma finds a champagne cork, which brings her back to happier times with Simon when they talked about how to be good parents to Tom.

Later, Gemma checks on Tom but sees he's not in his room. She tries to call him, but the call doesn't go through, leading her to think Simon has taken him away. James tries to calm her down and offers to go look for Tom, but she wants to find him herself.

Gemma keeps calling, and finally, Tom picks up the phone, but Simon snatches it from him and tells Gemma to leave them alone. Gemma can hear Tom asking for his phone back, but Simon ignores him.

Gemma spends all night looking for places they can possibly be and finally finds Tom looking at Simon, who contemplates throwing himself into the middle of the highway. Gemma tells Tom to stay away from the road and tries to convince Simon to stop what he's doing, because the consequences would harm not only him but also Tom, and the drivers and passengers of any cars involved. But does Simon care? No. He grabs her and intends to bring her with him, jumping into traffic. She fights back and pushes him away. Just as a car is about to hit him, Gemma manages to pull him back, painfully realizing she has two sons. She tells Simon something that convinces him enough for them to leave the scene and go to a diner together. It's finally revealed what Simon told Tom: Gemma used to have severe postnatal depression and once said she wanted Tom to die. Gemma had to undergo treatment and leave Tom with Simon, but Simon told Tom that Gemma hated him, tried to hurt him, then abandoned him, and Simon had to quit his job to take care of Tom. Gemma explains herself and tells Tom she always loves him and will always care for him. She then leaves the table to go to her car and gets all the needles with euthanasia drugs, goes to Simon's room, and lays them all out on the coffee table. This is likely what she told Simon she would do to convince him not to jump into the traffic in front of Tom. She comes back to the table and tells everyone she paid for Simon's room and he should think it through. Simon says goodbye to Tom and tearfully apologizes to him. Gemma and Tom leave and drive away, but as Simon starts injecting himself, Gemma opens the door and goes in. she has something to tell simon and tells him and want him to make the decision himself. Gemma tells Simon about how painfully her parents died and that injecting himself with the medicine isn't painless either. She tells him that she had wanted to drown herself but realized it would be selfish. When the conversation ends, Gemma goes outside only to find Tom gone. She tries to call him, only to discover his phone in the car along with a voicemail from him stating he's leaving because he has had enough of her and Simon. Gemma looks around with the police but can't find Tom anywhere. She returns to Simon's room, but he isn't there either, and Gemma cries in despair. Tom is reported missing, and Gemma regrets what she did. Speaking to the camera about her mistakes, Gemma asks Tom to return whenever he is ready.