苏格兰爱丁堡，雷登（伊万·麦克格雷格 Ewan McGregor 饰）、土豆（艾文·布莱纳 Ewen Bremner 饰）和病仔（约翰尼·李·米勒 Jonny Lee Miller 饰）三个青年过着混沌糜烂的生活，他们吸毒、滥交、诈骗无所不作，而在如此肆无忌惮挥霍青春的过程中，毒品成为一切万恶之源。
雷登对之亦爱亦恨，试图戒毒却最终重蹈覆辙。在一次纵情狂欢后，他们三个不知谁和少女爱丽森（Susan Vidler 饰）所生的婴儿死去。以此为开端，噩梦真正降临。土豆抢劫时锒铛入狱，雷登吸食毒品过量被送往医院抢救，后被强制戒毒。恐怖的幻觉和心底生气的恐惧迫使他不得不和毒品一刀两断。看似美好的新生活，但往日狐朋狗友贝格比（罗伯特·卡莱尔 Robert Carlyle 饰）等找上门来，再度给他带来无限的烦恼……
Heroin addict Mark Renton and his circle of friends are introduced: amoral con artist Simon "Sick Boy" Williamson (also an addict); slow-witted, kind-hearted Daniel "Spud" Murphy (another addict); clean-cut athlete Thomas "Tommy" MacKenzie; and the aggressive and pugnacious psychopath Francis "Franco" Begbie; picking fights with anybody who gets in his way.
It has been 20 years since Mark "Rent Boy" Renton stole from his friends the money they had made in a drug deal and fled the country. He has apparently made a decent – but unfulfilling – life for himself in Amsterdam, and returns to Edinburgh to make contact with those in his former life. Daniel "Spud" Murphy continues to struggle with his heroin addiction, which has caused him to lose his construction job and estranged him from Gail Houston and their son Fergus. Simon "Sick Boy" Williamson, now a cocaine addict, runs the Port Sunshine pub he inherited from his aunt, and with his Bulgarian girlfriend Veronika attempts to blackmail men by luring them into sex videos. Francis "Franco" Begbie is serving a 25-year prison sentence and is denied parole due to his violent temper.