Laura (Celia Johnson) is a housewife living in the suburbs outside London. She has a routine of going into town once a week by train to shop and watch a movie by herself. On one of these outings she runs into Alec (Trevor Howard) when she has a bit of dirt in her eye and he helps her remove it. They talk a bit afterwards and she learns he is a doctor and they're both married and both have small children. Eventually they start to see each other regularly, as friends, but they find that they are growing increasingly attracted to each other, and are both troubled by this.