When her alcoholic boss Andy is sacked, lazy Hannah seeks to impress his successor Annette Walker by claiming that, like Annette's son Charlie, her brother Dan is also in a wheelchair. In fact he is a selfish, immature scrounger, though he hits it off with Annette and Charlie despite overdoing his account of his 'accident'. Whilst Annette and Hannah get drunk at a conference, and have a threesome with a young waiter, Dan joins Charlie's wheelchair basketball team and scores the winning goal - though he betrays his deception by getting up to do a victory dance. However the threat of the threesome being exposed means that Annette allows Hannah to keep her job.

When Hannah's best friend Sadie returns from holiday with her handsome vet boyfriend Rich, announcing their engagement Hannah is jealous though she does attend the engagement party, where her rude present is not rapturously received. Dan warms to Rich who gives him a job as his receptionist, sadly unaware of how gormless he is. Hannah persuades Sadie to have a girl's night out and nearly kills her when she drugs her drink whilst Dan's total stupidity costs Rich his practice and the couple break all ties with the siblings.

Hannah goes to give a careers talk at her old school and impresses pupil Ellie, whom she takes on for work experience. Ellie is enthusiastic and efficient and lazy Hannah exploits this though when Ellie fights back Hannah uses dirty tricks to get rid of her. Dan has accompanied Hannah to the school and befriended three thirteen-year-old nerds, whom he brings home to play games with. Learning that they have been bullied by the younger brother of the boy who used to bully him Dan organises a fight in the playground to get his belated revenge but is surprised when a teacher turns up to stop the fight, reveals his identity and tells Dan the real reason for his being bullied.

The siblings' mother, Marion, insists that Hannah looks after her for two days whilst she is temporarily blind after laser eye surgery, but Hannah feels enslaved by her. Dan dates Izzy, the free-spirited doctor he met at the STD clinic, and falls in love. Hannah and Dan take Marion to Izzy's party, where Hannah and Marion bond when they take revenge on Izzy's strait-laced flatmate Pete, though the bonding ends when Marion gets her sight back and is not happy for Hannah to attend her Tae-Kwan-Do class. Dan attempts to prove to Izzy that he is a sexual being, but it ends horribly when he electrocutes himself with two dildos wired to a car battery.

High-flyer Gavin from the flat below asks Dan to feed his tropical fish whilst he is away. Miraculously the fish survive but, having the key to the flat, Dan passes himself off as Gavin, throwing a party at the flat. Here he has sex with Gavin's ex-girlfriend, before the real Gavin returns and throws him out. Hannah falls for busker, and ex-rock star, Bryn, now a born again Christian who has eschewed sex before marriage. Desperate to get into his pants, Hannah reunites his old group but still misses out as now he only wants sex with groupies.

Hannah and Dan attend the funeral of their old drama teacher Mr Balcombe, where Hannah is thrilled to see Adam Piper, the boy who gave her her first kiss, and Dan meets his equally brain-dead friends Jack and Sheriff, who egg him on to do stupid things - like ingesting all of Mr Balcombe's medication. Hannah seduces Adam, but is dismayed to learn that he did not give her that first kiss and is thrown out for trying to find out who did. Dan is too ill to help after swallowing all those pills.