In Book III Hannay and his friends sail to the Island of Sheep, and meet Haraldsen and Anna there. One day Peter John and Anna go canoeing, and come upon a Danish trawler, the "Tjaldar". They meet the real villain, Jacques D'Ingraville, on board and are captured, but one of the crewmen, Martel, helps them to escape. They arrive back at the island and summon the whaling crew of the "Grind" for help. Meanwhile, Hannay, Lombard, Geordie Hamilton and Haraldsen receive a message from Morag that they are about to be attacked. They barricade the house. D'Ingraville, Martel and a Spaniard, Carreras, arrive to offer terms. Hannay lets Martel into the house to negotiate and Martel reveals himself to be Sandy Clanroyden. Clanroyden assures Hannay that the children are all right and then rejoins D'Ingraville, after which his cover is blown by Haraldsen. Clanroyden manages to escape and joins Hannay on the roof. Haraldsen goes berserk and throws D'Ingraville to his death off a cliff. Anna and Peter John then arrive with the crew of the "Grind". The criminal gang is subdued. Lancelot Troth, Albinus and Barralty make peace with Haraldsen, and are invited to dinner with him. Clanroyden gives his jade tablet to Troth.