Albert Carter, a philosophy student, takes a vacation job as part of a team painting a large road bridge. He becomes fascinated both by the repetitive nature of the process and the freedom it gives him for quiet contemplation, detached from the real world far below. However, his father, a down-to-earth, prosperous paint manufacturer, is determined that Albert should get a 'proper job' in the family firm. Albert is (reluctantly) engaged to Sophie, an aspirational middle-class girl favoured by his family, though he is secretly carrying on a love affair with the family maid, Julie.
Albert's father has developed a new, long-lasting paint which the Town Council decide to adopt for the bridge. They are persuaded by Fitch, the Borough Surveyor, that only one painter is now needed, and an ecstatic Albert is offered the job. However, family pressure and a guilty conscience confront him with a dilemma: to follow his dreams, marry the now-pregnant Julie, and dedicate his life to the bridge; or to face reality, marry Sophie, and settle down to a comfortable life in the family business.
The second act sets out both courses of action in alternating (and sometimes simultaneous) scenes. One scenario sees Albert’s marriage to Julie gradually falling apart as he becomes engrossed in his solitary routine on the bridge. Alternatively, Albert marries Sophie, but his equally obsessive attention to the details of factory management eventually drives her into the arms of Jonathan, the posturing political activist. Meanwhile, the Town Council have discovered that Fitch's miscalculations have caused the bridge to deteriorate alarmingly. In desperation, they despatch an emergency army of painters to take over, but their arrival on the bridge triggers a catastrophe. The alternative courses of Albert's life finally conjoin as the weakened bridge collapses, and both Sophie and Julie are left alone to pick up their lives again.