Thelma and Bob are on honeymoon in Norway but Bob has omitted to tell his wife that he gave Terry a key to the house whilst they were away. Terry makes several unsuccessful calls but finally gets through and tells Bob not to worry. In returning the call Bob learns that Terry and Thelma's sister Susan are in the house together. Thelma is far from pleased.
Back from honeymoon Thelma is far from pleased to learn that Terry is seeing Susan, who has a boyfriend Peter back in Canada. Then Terry comes round for a heart to heart with Bob, telling him that he is afraid things are getting serious between him and Susan. However he is ultimately relieved to hear that Susan is going back to Peter in the knowledge that things did not go too far with her.
Bob is working himself too hard whilst Terry is enjoying a life of leisure. Bob can only just stay awake when he meets Terry and a glamorous girlfriend in a restaurant but soon Terry is bemoaning his lack of ambition so Bob sends him for a job interview. He doesn't go but spends the fare on a bet, which sees him nicely in pocket. Now it's Bob's turn to reflect on his carefree bachelor days when he had no responsibility.
Bob is arrested for being over the limit whilst driving home and taken to the police station, where he meets Terry, who has been arrested for fighting at a football match. As Bob is scared that he will lose his licence, Terry agrees to change identities with him for the blood test. Bob subsequently spends a night in the cells (as Terry), and then appears in court and is fined. Just when they are celebrating the success of their swap, Bob realises that Terry had also been drinking the previous evening and the blood sample he gave (as Bob) is even more likely to prove ...
After Terry is winded playing football Bob accuses him of being out of shape and challenges him to a cycle race to Berwick. Needless to say both cheat, hitching lifts and sabotaging each other but they duly arrive in Berwick. Too tired to cycle home, they go to the station only to find there are no trains till next day as it's a Sunday.
Whilst he and Thelma are on holiday Bob lets Terry stay at their house in exchange for doing some work on the house. However, Terry is side-tracked by Sandra, an attractive neighbour, who asks him to fix her taps but whose bathroom he accidentally floods whilst she - almost - seduces him. Bob and Thelma return homer unexpectedly and are injured, due to Terry's half-completed handiwork, whilst Bob gets punched by Sandra's irate husband who has mistaken him for Terry.
Terry and Bob are staying at a country hotel for a fishing weekend, Bob feeling guilty about not bringing Thelma, when they meet Thelma's father, accompanied by his secretary Beryl for an illicit weekend. When Thelma turns up to say she misses Bob she jumps to conclusions and assumes he is cheating on her but Beryl saves the day - to Terry's advantage though Thelma's father is disappointed.
After a big row with Bob Thelma goes back to her parents and Terry comes round to advise Bob on how to win her back. Initially he suggests Bob play it cool but Bob is not convinced so they decide he should be masterful. When he hears somebody in the bedroom he assumes it to be Thelma and locks her in to teach her a lesson - but it turns out to be the cleaning lady. However when Thelma comes to collect her things she locks Bob in the bedroom to show who's boss.
Thelma is still absent and Bob is desperate to keep the fact from the badminton club. Terry moves in to look after him but his slovenly ways annoy Bob, who writes a letter to Thelma, saying he wants her back. Terry tries to deliver it to Thelma's colleague, who mistakes him for Bob and refuses to accept it but when Terry tries to give it to Thelma she accuses Bob of being too cowardly to deliver himself and rips it up.
As Thelma is still at her parents Terry moves in with Bob but soon annoys him with his slovenly ways. Terry sees that Bob and Thelma should reconcile and goes to see her, painting a picture of an unhappy Bob. When he eventually brings her to the house they are shocked to see Bob with his head in the gas oven and fear the worst - though he is only cleaning it after Terry has made a mess inside it.
Terry is up in court for fighting in the pub with local lad Dougie Scaithe and is found guilty and is fined. Unaware that Terry and Dougie have patched it up, Bob confronts Dougie and also gets into a fight with him, landing before the same magistrate who fined Terry. In the pub the likely lads argue over which is the better fighter and decide to have a practical demonstration. Unfortunately the magistrate just happens to be in the pub as well and witnesses their set-to.
Terry hears that his great uncle Jacob has died in the rest home where he lived and where he made life difficult for everybody with his selfishness. Terry sees this as individualism but, after he has accidentally brought the cremation forward, he and Bob meet a man from whom Jacob perpetually sponged. Bob draws comparisons between the two with himself as the stooge and Terry as the user and tells him he is planning to see less of him, though Terry has already told Thelma they will be off drinking together.
Terry has passed his driving test and is working as a mini-cab driver. It's Christmas and Bob and Thelma are off to a dance and have Terry as their cab driver. However Bob and Thelma row when he meets up with an old girl-friend. She asks Terry to drive her home, unaware that Bob & his ex are hiding in the back. The ex forces Bob to drive her home, leading Terry to believe somebody has stolen his car.