Hunting Gumnor is a story about the sea and sea-people, but it is also a story of mystery, friendship and isolation. To many people, the vast deep seas that wash our planet are a source of endless fascination and adventure, drawing the imagination to them like no other feature of Earth.
Rarty Boofus, the young girl at the centre of the novel, lives with her parents in a lonely island community far away from the nearest mainland. Rarty's present life and her future are linked to ships and the sea and she cannot imagine anything else.
The sea, of course, is a dangerous place and when the fogs close in, Rarty's island home becomes a perilous trap to ships trying to negotiate the harbour. Rarty's father has the job of warning any approaching ships about the dangers of entering the island waters when fog is expected. Other harbour masters use a mechanical foghorn to alert distant ships to danger, but Rarty's father uses something very different to do the same job.
For many years, the harbour has been the home of Gumnor, one of the last foghorn whales to survive hunting and extinction. The Boofuses look after Gumnor like any other family would look after a pet dog or cat. Gumnor, the last of the cetylareans, is kept in the harbour in chains, but Mr Boofus knows that she stays there because she wants to, not because of the chains. The ocean would be a lonely place for Gumnor now that there are no more foghorn whales left in the depths of the sea. She is better off where she is.
Marine experts have different opinions why foghorn whales give out a loud booming cry when fog is in the air. But for whatever reason, the cry acts as a shipping warning, and the islanders know it is a loud roar of loneliness.
Rarty and her father are both devastated when one day they discover that Gumnor has vanished from the harbour. The chains have been broken and the foghorn whale has disappeared. The search for Gumnor is on.