A scientist travels in the ship as a passenger. The captain of the ship does not agree to accommodate any more passengers, so the only way the boys may join the journey is to join the crew.
Roger defends a captured sperm whale against a group of sharks and later a pack of killer whales. This novel also explain how clever killer whales are.
The captain of the ship is a ruthless man who tortures and punishes the crew. He is beaten by Hal in a hand to hand fight. When an old sailor, who is pulled over the sea as a punishment, is eaten by a shark, the crew takes the control of the ship, confining the captain and his henchman in the cage.
In the end of the story, their ship was destroyed by a sperm whale and they were saved by a modern whaler with a whale-spotting helicopter.