Young factory worker Arthur (Albert Finney) works long and hard hours at his mindless job, but lives for his Saturday nights at the local pub. His rebellious nature leads him to do a number of questionable things, and his current girlfriend Brenda (Rachel Roberts) is the perfect example, as she is the wife of one of Arthur's co-workers at the factory. While still involved with Brenda, Arthur meets Doreen (Shirley Anne Field), and the two quickly enter into a relationship. Things become increasingly more complicated when Brenda tells Arthur that she's pregnant, and also confronts him about his relationship with Doreen. When his seemingly carefree life suddenly becomes more complicated, it is up to Arthur to cope with the challenges he faces.