John Duncan is a biologist. At the beginning of the story he gets a job with a paint company. His job is to ensure that the chemicals used in the company are safe.
John is widower, and he lives with his two children, 13 years old Andrew, and 16 years old Christine. For two years he has been unemployed, and getting this job makes a difference to both him and his children. The family move into a house by the river, near the paint factory. They can go out in their boat and look at the seals on the sandbank near the mouth of the river.
But John discovers that some of the chemicals from the factory are polluting the river. These chemicals are particularly dangerous - they can cause deformities in baby rats, and perhaps in people. He points this out to the company, but it would be very expensive to stop the pollution - too expensive. John has a choice: either he tells the newspaper about his discovery - and loses his job. Or he keeps quiet, and keeps his job. He chooses to keep quiet.
But after some years the pollution does start to cause problems, and these problems are published in articles in the local newspaper, written by Simon, a journalist who is engaged to Johns daughter Christine. It is not enough for John to keep quiet: now he has to start telling lies, to say that there is no pollution problem.
Christine and Simon become involved in a campaign against the factory, and one day, demonstrating from a small boat in the river. Christine, who is pregnant, falls in, and is nearly drowned. At a Public Inquiry into the pollution, John is forced to admit that there is a serious problem - and that his daughters baby is it a risk.
At the end of the story, John has lost his job - and Christine will no longer speak to him. And neither he, nor we, know whether her baby is healthy or not.