Pete and Jenny have separated, so he has been living at Adam and Rachel's. He moves back in with Jenny as her lodger when Adam and Rachel tire of his uncleanliness. As Karen and David return home with their new baby twins, Ellie and Olivia, Heather, Karen's ex-pat mother, arrives from Spain. At a dinner party, she takes a liking to Felix, one of David's clients. Jenny has also been invited, and is smitten with Robert, another client. Pete prepares breakfast for Jenny on their anniversary but is saddened when she receives flowers from Robert. Rachel tells Adam that her period is late.
Pete starts searching for a place of his own as Jenny and Robert start going on dates. He eventually finds a house-share with Matthew, a middle-aged divorced man who he is later shocked to discover is gay. Rachel's pregnancy turns out to be a false alarm. A visit to the doctor informs them that Rachel's inability to conceive might be related to her abortion. Jessica, a local political activist, arrives on the Marsdens' doorstep. David attends a local residents' meeting and becomes attracted to Jessica.
Pete and Ramona start seeing each other after an encounter in the park, and Jenny has to deal with her friends' reluctance to get to know Robert. Adam and Rachel attend their first appointment for Rachel's intracytoplasmic sperm injection. Heather smacks Josh but makes up with Karen and later returns to Spain. David organises his own 40th birthday party and decides to make it fancy-dress. At the party, he kisses Jessica, and Jenny becomes jealous when she sees Pete and Ramona dance. The next morning, David is surprised to find a Harley-Davidsonmotorbike in the kitchen.
Pete and Ramona spend more time with each other, and she watches him play on Matthew's all-gay football team. Karen meets up with her old college friend, photographer Miles Brodie, as David spends more and more time with Jessica. The cost of Adam and Rachel's ICSI treatment begins to mount. Results from a scan come back, and it is revealed that Rachel is suffering from "partial Asherman's syndrome" resulting from her abortion. Later, he proposes to her.
Adam and Rachel's friends show public support when they announce their engagement, but secretly believe they are doing it for the wrong reasons. Karen becomes jealous of Jenny when she takes charge of planning Brodie's photography exhibition. David and Jessica book into a hotel for a dirty afternoon, and Pete begins chatting with "Girlpower", a woman on an Internet chatroom. She asks to meet him at the school where she works, where it turns out he was set up by two schoolgirls. However, he does get a date with their teacher, Emma. After abandoning the idea of a long engagement, Adam and Rachel decide to get married as soon as possible.
Pete and David take Adam on a stag weekend to Belfast and Portrush, where he grew up. At a surprise party, he is reunited with his old girlfriend, Jane Fitzpatrick, and later drunkenly falls asleep in her bed. Pete discovers David's affair with Jessica, and makes him promise to break up with her when they get home. Meanwhile, Rachel has taken Karen and Jenny to a health spa. Jenny lets slip that she once kissed Adam and Rachel is furious. They make up and decide to meet up with their partners in Northern Ireland. Rachel tells Adam that she knows about him and Jenny and he does not tell her that he kissed Jane the night before.
Jenny takes charge of planning Adam and Rachel's wedding as Adam buys Rachel an unattractive engagement ring. David unceremoniously breaks up with Jessica in a restaurant, where they are seen by Robert. After Karen is arrested for tackling a car thief, David takes her out to dinner, where she begins to suspect something is wrong. An argument over the engagement ring leads Adam and Rachel to scale back their wedding plans; they opt for a simple register office ceremony instead of at a large country house. Pete, enjoying his dates with Emma, asks Jenny for a divorce.
On the morning of the wedding, Pete wonders if divorcing Jenny is the right thing to do. As Robert is moving his things out of Jenny's house, he tells her that David is having an affair. She tells Rachel and they both wonder whether to tell Karen. Adam arrives late to the registry office after Pete forgets to arrange for a car. The reception is held at Karen and David's. David realises that everyone except Karen knows about the affair, and tells her himself. He offers to leave but she decides that they should stay together for the kids. The episode ends with the couples watching Adam and Rachel's wedding video, filmed by Pete. Though David and Karen's marriage appears to be over, Pete and Jenny are back together.