Section 1: Kicking
Mark and Simon (a.k.a. Sick Boy) are watching a Jean-Claude Van Damme video when they decide to go buy heroin from Johnny Swan (also called "Mother Superior") since they are both feeling symptoms of withdrawal. They cook up with Raymie and Alison. After being informed that he should go and see Kelly, who has just had an abortion, Renton goes home to finish his video instead.
Mark initially tries to come off heroin by acquiring a bare room and all the things he will require when coming down (canned soup, headache medicine, and pails for vomit). When withdrawal begins to set in, however, he resolves to get another hit to ease the decline. Unable to find any heroin, he acquires opium suppositories which, after a heavy bout of diarrhoea, he must recover from a bookie's lavatory. Simon attempts to pick up girls while being annoyed by Mark, who wants to watch videos. Sick Boy loses Renton and launches into an internal monologue that is self-glorifying and nihilistic.
The chapter "It Goes Without Saying" opens with the death of an infant, Dawn, whose mother Lesley is a heroin addict and acquaintance of the main characters. The cause of death is unclear; characters speculate that it may have been a cot death or caused by neglect. The Skag Boys are unsure of how to respond. Sick Boy becomes notably more emotional and distressed than the others and eventually breaks down as well, stating he is kicking heroin for good. Simon does not explicitly state that he was the child's father, playing to the title of the story. Mark wants to comfort his friend, but is unsure how and cooks a shot for himself in order to deal with the situation. A sobbing Lesley asks him to also cook her up a hit, which Mark does but makes sure he injects himself before her, stating the action "goes without saying".
After an argument with his girlfriend Carol, Second Prize meets Tommy in a pub, and Tommy confronts a man who is punching his girlfriend. They are shocked to find the woman supports her abusive boyfriend instead of her would-be liberators by digging her nails into Tommy's face, inciting a brawl. While the couple slips out unnoticed, Tommy and Second Prize find themselves taking the blame for the whole affair from the pub locals.
The section ends with Spud and Renton, who have been assigned interviews as part of their job-seeking benefits, deliberately failing to get jobs, while attempting to obscure that it is deliberate.
Section 2: Relapsing
Renton, Begbie and their girlfriends meet up for a drink before going to a party, but it ends when Begbie throws a glass off a balcony, hitting someone and splitting open their head, setting off a huge pub brawl.
In another scene, Tommy comes around to Renton's flat (shortly after Renton relapsed) after being dumped by his girlfriend. Renton reluctantly gives him some heroin, setting off Tommy's gradual decline into addiction, HIV/AIDS, and later, death.
Later, Renton's brother Billy and his friends Lenny, Naz Peasbo, and Jackie are waiting for their friend Granty to arrive for a game of cards, as he is holding the money pot. They later find out that Granty is dead and his girlfriend has disappeared with the money, prompting them to beat Jackie, whom they knew to have been sleeping with her.
Section 3: Kicking Again
Begbie and Lexo have pulled an unknown crime, so Begbie decides to lie low in London with Renton. The chapter called 'Inter Shitty' covers their train journey.
Spud manages to kick heroin, and visits his grandmother, where his mixed-race uncle Dode is staying. He recounts the trouble that Dode has had with racism growing up, particularly an event when he and Spud went to a pub and were assaulted by white power skinheads. This abuse led to a fight, which left Dode hospitalised, where Spud visits him.
Renton has kicked heroin and is restless. He picks up a girl at a nightclub, Dianne, unaware that she is only fourteen. He is later forced to lie to her parents at breakfast the following morning. Despite his guilt and discomfort, he sleeps with Dianne again when she shows up at his flat. Spud, Renton and Sick Boy take some ecstasy and stroll to the Meadows where an excited Sick Boy and Renton try to kill a squirrel but stop after Spud becomes upset by their actions towards the animal. He states to the reader that you can't love yourself if you hurt animals as it's wrong and compares their innocence to that of Simon's dead baby Dawn. He also states that squirrels are "lovely" and "free" and that "that's maybe what Rents can't stand" indicating Mark envies those he feels are completely unbound and free. Mark is ashamed and Spud forgives him quickly and the pair embrace, before Simon breaks them up.
Section 4: Blowing It
Renton and Spud are in court for stealing books. Renton gets a suspended sentence owing to his attempts at rehabilitation, while Spud is sentenced to ten months in prison. Renton relapses and has to suffer heroin withdrawal at his parents' house, where he experiences hallucinations of the dead baby Dawn, the television programme he is watching, and the lecture provided by his father. He is later visited by Sick Boy and goes out to a pub with his parents, whose unnerving enthusiasm acts as a veneer for their authoritative treatment.
Renton's brother Billy dies in Northern Ireland with the British Army. Renton attends the funeral; there, he almost starts a fight with some of his father's Unionist relatives, and ends up having sex with Billy's pregnant girlfriend in the toilet. Renton discusses the hypocrisy of Unionism and the British in Northern Ireland.
Section 5: Exile
Renton is stranded in London with no place to sleep. He tries to fall asleep in an all-night porno theatre, where he meets an old homosexual named Gi, who lets him stay at his flat. Later, Renton, Spud, Begbie, Gav, Alison and others venture out for another drink and something to eat. Spud and the others reflect upon their sex lives.
Section 6: Home
Spud, Begbie, and a teenager have engaged in a criminal robbery. Spud recounts the crime and comments on Begbie's paranoia and how the teenager is likely to get ripped off by the pair. Gav tells Renton the story of how Tommy died of toxoplasmosis after attempting to rekindle his relationship with his ex using a kitten.
The group attends Matty's funeral, where they reflect on his downfall, and what may have caused it. Later, Renton returns to Leith for Christmas and meets Begbie, who beats up an innocent man after having seen his alcoholic father in the disused Leith Central railway station. He visits a former drug dealer, Johnny Swan, who has had his leg amputated as a result of heroin use, and he visits Tommy, who is dying of AIDS.
Section 7: Exit
Renton, Sick Boy, Begbie, Spud and Second Prize go to London to engage in a low-key heroin deal and see a Pogues gig. The book ends with Renton stealing the cash and going to Amsterdam. Renton thinks to himself that he will send Spud his cut, as he is the only 'innocent' party.
