Gary has a dream in which he and Dorothy are at the altar, both pregnant. After initial repulsion he starts to warm to the idea of being a father, buying a huge cuddly rabbit, but after seeing the contents of his brief-case Dorothy decides he is too immature to father her children. Tony is given the key to Deborah's flat to let in the boiler repair man but reads her diary and upsets orange juice into her knicker drawer, necessitating a trip to the laundrette and - after all the colours have run - fabricating a burglary though Deborah does not buy it.
Tony annoys Deborah with his lack of attention span whilst they are watching television, leading to her declaring that she is fond of him but cannot date him because of his immaturity. To impress that he can be responsible he takes to doing voluntary work in an old folks' home - only to find that Deborah has another boyfriend. Gary becomes suspicious meanwhile that Dorothy is seeing somebody else and shadows her, using a number of not very convincing disguises.
Dumped by Dorothy for her new boyfriend Jamie Gary is extremely depressed and the noisy love-making of Tony and his girlfriend Jill does not help. When Deborah and her new man invite Dorothy and Jamie to dinner Gary tries to counter with a party of his own but nobody turns up and the food is the left-overs from the pub. Drunk and desperate Gary crashes the party upstairs, making a fool of himself, and has to be rescued by Tony - though, since Jill has left him because he will not throw out his girlie magazines - Tony ends up getting even drunker with Gary.
Whilst Gary wallows in the self pity of being dumped by Dorothy Tony has three girls on the go and has to work out a system to stop them meeting. For Father's Day Tony arranges for Gary's dad to visit but they do not get on and the visit is a disaster. Dad also interferes with Gary's effort to find a 'Plus One' to accompany him to Dorothy's engagement party to Jamie but ends up dateless. However Dorothy turns up to comfort him, having split up with Jamie.
To celebrate getting back together again with Gary Dorothy cooks a meal but first Gary and Tony repair to the pub where landlord Les invites them to sample his guest ales. Inevitably the pair get very drunk and, when they return home, find that they have been locked out. Gary breaks in and crawls into bed with an unimpressed Dorothy but Tony ends up in the shed.
Dorothy is having bed rest after having her appendix taken out but Gary's nursing skills leave much to be desired as he pretends the appendix is a moustache and races around the flat in her wheelchair. Dorothy gets revenge by pretending Gary has killed her. Tony finds he needs to wear glasses but, after everybody has laughed at him, opts for contact lenses instead. They still blur his vision though, especially when Gary offers him the appendix claiming it is a pickled chilli.
Whilst Gary and Deborah are both away for the weekend Dorothy and Tony are left alone together. Tony gets tooth-ache and, having a fear of dentists, attempts his own extraction by tying the tooth to the door and pulling it shut. After Dorothy has brought him a pain-killer they somehow end up in bed together. Unfortunately Gary returns early and surprises them.