Glasgow, the late 1960s. Lex MacLean buys a skeleton from a local boy and gives it as a birthday present to his artist brother Alan. Eldest brother Bobby kills Lex's goldfish by deliberately overfeeding it. During the night, the boys' mother Lorna rushes to comfort Bobby, who is tormented by nightmares about his own death. At school, Lex is introduced to Alan's friend Fabio, who asks him about his drawings.
Later, at the funfair, Lex witnesses Bobby's gang, the Glen, in a skirmish with arch rivals the Tong. At a family gathering, Lex sneaks drinks of alcohol while Uncle Andrew - who has arrived from Seattle - holds court. Once everyone has left, Lex throws a drunken tantrum and attacks Bobby. The following day Bobby gives Lex an air pistol as a peace offering. Lex accidentally shoots a footballer in the eye and he and Alan are forced to flee from a mob of angry team-mates. Later he discovers that the injured party was Malky Johnson - notorious leader of the Tongs.
On his paper round, Alan bumps into Joanne, an old primary school colleague, who asks him out on a date. Lex and Alan go to the home of Glen leader Charlie Sloane and plead for protection from a vengeful Malky. Charlie invites them to join his gang. Joanne demands to know why Alan stood her up on their date. Back in his room, she shows off a ring from Malky Johnson, who she claims is obsessed with her. While shoplifting from a clothes store, Lex spots Joanne kissing Alan. He tells her he is prepared to keep quiet about her affair in return for favours.
In a local nightclub, members of the Tong square up to Bobby, who escapes with Lex's help through a toilet window. Lorna is furious that they have returned home so late and orders the boys to their room. Bobby is spooked by Alan's skeleton and proceeds to smash it up with a hammer. Lex visits Fabio to show him some of his drawings.
After leaving his house, Fabio is attacked by members of the Glen. A showdown between the Tong and the Glen takes place after the former are 'jumped', and Bobby smashes a brick into Malky's face. Upon hearing about Fabio's horrific attack, Lex vows revenge on Charlie. Arriving in Tong territory, he befriends Malky's step-brother Gorbals and says that he wants to join the Tongs. He informs a suspicious Malky that Charlie goes skating every Saturday morning with Joanne. After Lex has left, Malky dangles Gorbals from a high-rise balcony and forces him to reveal his new friend's identity. He discovers that Joanne is dating Alan behind his back.
Alan shows Joanne a portrait he has drawn of her. He becomes angry upon hearing of her involvement with Charlie, telling her she can't date every hardman in Glasgow. She storms off. At the ice rink, Lex watches helplessly as Tong hitmen, following Malky's orders, slash Bobby to death on the ice. Lorna is called to identify the body and, in a fit of grief, urges her remaining sons to hunt down the animals who murdered their brother.
Gorbals gives Lex a knife and warns him that Malky is out to get him and Alan. Lex uses the knife to attempt to break into Malky's flat, but is forced to flee. Malky confronts Gorbals about Lex's whereabouts. While Malky is sleeping, Gorbals interferes with the gas cylinder, causing a leakage. Malky wakes and lights a cigarette, blowing himself up. Hearing about Malky's death, Lex rushes to the scene and is informed by Gorbals about the night's events. On his own with Joanne, Lex hears that she is planning to move to London to study. Uncle Andrew subsequently marries Lorna, while Alan goes to art school.For all his dreams, Lex is relieved to discover he is still a boy.
