Martin meets a nurse named Clare, who agrees to go out with him. She tells him that she wants to lose her virginity. After a few mishaps, Martin finally makes love to her. Meanwhile, Matthew decides to stay in bed, and Mandy resolves to become celibate.

Martin can't stop talking about his newfound sex life. Matthew confesses to Mandy that he's terrified of going out of the house, so she arranges for him to meet her psuchologist friend Jason. Unknown to Matthew, Jason is gay and, after talking to Matt, he tells Mandy that he's fallen in love. Mandy starts an Italian evening class and her tutor, Mario, shows an interest in her. When she tells him that she's celibate, he misunderstands and thinks she's trying to say that she's a virgin. Then Martin and Mandy discover Matthew in bed with Jason....

Jason manages to persuade Matthew to go out to the park and, later, to a gym. WhenMatt shows Marco a video of Mandy having sex, Marco realises that she isn't a virgin and decides he's no longer interested in her. Meanwhile, Martin has become very insecure about his relationship with Clare. A combination of paranoia, jealousy and drink leads him to make a complete fool of himself. Matt finally manages to go out on his own, on a trip to a local shop. Unfortunately, the shop is raided by a masked gunman, so Matthew decides that he'll never go out again!

Mandy is visited by her old boyfriend Stoat. When the flatmates discover that he's escaped from prison, Stoat ties up Matthew, Martin, Jason and Clare. He takes Mandy into her bedroom and they end up having sex. Mandy ties Stoat to the bed and gets his gun, then releases her friends. Clare tells Matt that Jason is gay. Jason leaves and Clare dumps Martin.

Martin is very depressed about the end of his relationship with Clare; Mandy has a close encounter with Brian Kennedy, a lecturer from her old university; Martin and Mandy find out what Matthew has been writing in his secret journal.

Martin realises that Clare left him because he's boring. He starts a voluntary job, working for a telephone helpline for distressed people. He gives his home phone number to Tesni, one of the helpline's clients. She rings the flat while Matt is at home alone and, thinkng that Matthew is Martin, she threatens to commit suicide unless he visits her home. Matt goes round to see her but, when he gets there, he collapses and has to be rushed to hospital. Martin arrives at the hospital, looking for Clare. Mandy also turns up, with her latest boyfriend. Matt meets a red-haired student named Susie and falls in love with her.

Matt has taken up palmistry as an aid to seduction; but how can he seduce women without leaving the flat? Mandy has built up debts of over 9000 pounds using her credit cards, and now a female debt collector is on her trail. Mandy's money problems are solved by an interest-free loan from her millionaire boss, Archie. Meanwhile, Martin hears news of Clare.

Martin bumps into Clare in the video shop and discovers that she has a baby, Rosie, and that he's the father. Martin pays a surprise visit to Clare's home, but finds her with a man. After he rants about how wrong it is for anyone to come between a father and his daughter, he discovers that the poor man has only come round to fix the washing machine. Clare tells Martin that she doesn't want him involved in bringing up his daughter, so Martin sees a lawyer to find out if he has any legal rights where his daughter is concerned. Mandy is still going out with Archie. When he calls round to pick Mandy up for a date, Martin tells him that Mandy is only interested in him because of his money. Next day, Archie tells Mandy that he's in love with her and wants to marry her. Finally, Clare relents and tells Martin that she wants him to be Rosie's dad after all — and lets him look after the baby while she goes out on a dinner date.

Matt declares his ambition to join the Marines in memory of his brother, Danny, who died in a road accident days before he was due to qualify as a Marine. Mandy and Archie go to bed, but Archie turns out to be impotent. Matt builds a jungle assault course in the flat; he also tries to have sex with a vacuum cleaner and gets stuck. Martin calls Clare and she comes around to help; then Mandy arrives home with Archie and a group of friends from his days in the Marines. Archie reveals that HE had a brother named Danny who died just before he was due to become a Marine. Later, Archie finally manages to overcomes his impotence.

Mandy has to cook dinner for Archie's mother and sister and she's getting worried about it. Martin drives Matt crazy going on and on about baby Rosie. Clare tells Martin that she can't see him as a proper father because he's not much better than a vegetable. Mandy wants to cook some crabs, but they're still alive and she can't manage to kill them. It looks as if the dinner party will be a total disaster. She gets drunk and passes out, leaving Martin to prepare the meal using some of his mother's frozen meals. Archie's sister Lulu gets the idea that Rosie is Martin and Mandy's baby. Mandy unwwittingly reveals details of her past to Archie's mother, who threatens to tell Archie. Clare tells Martin that she's planning to emigrate to Australia. Archie tells Mandy that he doesn't mind about her past.

Clare tells Martin that she's going to Australia with her new boyfriend, Shane. Martin decides to consult a lawyer to see if he can prevent Rosie being taken out of the country.

Matt meets Laura, who's just moved into the flat upstairs. He tries to impress her, but only succeeds in making himself look foolish. Then he finds her on the stairs outside the flat, upset after a row with her husband. He invites her in and comforts her. She drags him into his bedroom for an afternoon of wild sex.

When Mandy and Martin come home from work, Matt boasts about his new affair, but they don't believe him.

Clare is angry when she learns that Martin is taking legal action to stop her from taking Rosie to Australia. Martin eventually fires his lawyer when he decides that he's "mad". He decides to kidnap Rosie instead and take her to Brazil, but changes his mind after seeing Clare and Rosie together.

Matt persuades Martin to hide in the living room when Laura comes round. They have sex on the sofa which Martin is hiding behind. When Mandy comes home, Martin tells her that Matt was telling the truth, but Mandy still isn't convinced. Matt starts shouting about his activities with Laura and her husband hears him. When he comes downstairs, Martin answers the door and gets punched instead of Matt.

Martin gets a postcard from Clare, telling him that she's married Shane in Australia.

Everyone is preparing for Mandy's wedding. Archie has been set a series of "challenges" by his ex-marine chums, in preparation for his marriage. Matt has been persuaded to go to the wedding.

Martin goes to Mandy's hen night and meets a girl named Rachel, who's "almost exactly like Clare" (except that she isn't Irish, she isn't a nurse and her hair is the wrong colour). He arranges a date with her, during which he gives her a wig (similar to Clare's hair) and asks her if she'll speak with an Irish accent.

On the morning of the wedding, Martin gets a phone call telling him that the wedding limousine isn't available. He borrows an old Nissan and drives Mandy to the church. Matt travels in the boot. When they arrive, there's no sign of Archie. Then the best man arrives and tells Mandy that Archie has been killed in a car crash. She drives off at high speed, saying that she intends to crash the car and kill herself. Martin isn't keen on the idea, for obvious reasons, and manages to talk her out of it.

When they get back home, Martin gets a phone message from Rachel. She says that he's a "weird, twisted pervert" and she doesn't want to see him again. Apparently this reaction was caused by the nurse's uniform he'd given her as a present.

Mandy learns that Archie was killed trying to meet his final "challenge" - to get a speeding ticket on the way to his wedding.