Renton is not stupid. He knows that he must get away from his friends because they are a bad influence on him. But he is lazy and finds it difficult to stop using heroin. His parents worry about him and want to help him, but there is little they can do. Sometimes he tries to stop using drugs, but he can never quit for long.
Renton has a friend called Tommy who lives a healthy life free of drugs. He is interested in bodybuilding and is in love with his girlfriend Lizzie. But recently he and Lizzie have not been getting on so well because he went to a concert on Lizzie's birthday instead of celebrating with her. One day while visiting Tommy, Renton steals a video of Tommy and Lizzie making love together. When Lizzie finds out that their video has gone, she gets really angry and leaves Tommy. He is heartbroken and asks Renton to sell him some heroin to help him forget his troubles. Unfortunately his troubles are only just beginning. He gets infected with the AIDS virus from a dirty needle.
Renton and Spud get arrested for shoplifting, and they are sent for trial. T he judge sends Spud to prison, but not Renton. Instead his parents lock him in his bedroom to make sure he cannot get into any more trouble with drugs or the police.
One night at a disco Renton meets Diane. They go back to her house in a taxi and make love. Afterwards she tells him to sleep on the sofa in the corridor. The next morning he meets two people whom he mistakes for Diane's flatmates. They are in fact her parents, and Renton is shocked to find that Diane is still only a schoolgirl.
Renton decides to get away from his friends and leave Scotland. He moves to London where he works in an office. He starts saving money and lives a quiet life by himself. One day he gets a letter from Diane telling him that Begbie is wanted by the police in connection with an armed robbery. To his dismay Begbie comes to his door and says he is going to hide in Renton's flat while the police are looking for him. Soon Renton gets another unwelcome visitor, Sick Boy. The three of them live together, but life is not much fun for Renton; he returns home from work to find that they have sold his television.
The three men return to Edinburgh for the funeral of their friend Tommy who died from a horrible disease of the brain. He caught the disease from the kitten he had bought as a present for his ex-girlfriend Lizzie. She refused to accept it and so he had to look after it himself. Unfortunately he did not clean up its mess and dirt, and as a result he got sick.
After the funeral Begbie, Sick Boy and Spud tell Renton of a plan they have made. They want to buy some heroin from a man called Mickey Forester (who got it cheap from some Russian sailors), and sell it in London. They need four thousand pounds to buy the drugs, but so far they have only got half the money. They ask Renton for the rest. He tries to refuse but he is forced into joining them.
They travel down to London on the bus and go to a hotel where they meet the man who wants to buy the heroin from them. He pays them sixteen thousand pounds, so they are very happy. But soon their excitement disappears and they become very nervous. They do not trust each other and they all watch the bag containing the money in case anyone tries to run off with it.
In a pub Begbie attacks a man who was standing at the bar when Begbie tried to buy some beer. Spud tries to stop the fight but gets injured in the hand as a result. They leave the pub and return to their hotel room. Begbie goes to sleep on the bed holding the bag with the money in it in his arms. While the others are asleep, Renton gets up and has a drink of water. He looks at himself in the mirror and makes a decision. He takes the bag from the sleeping Begbie and moves towards the door. Just as he is about to leave the room, he notices that Spud is awake and looking at him. Without a moment's hesitation Renton walks quietly out of the room. He leaves some money in a locker for Spud and then sets out to start a new life far away from his old Edinburgh friends.