Erskine and Haber are sent aboard a schooner called the Klaraborg with four other men with sealed orders. When they are opened, the crew find that they are to enter Singapore harbour to sink merchant ships. When some things go wrong with the boat, Erskine suspects there is a saboteur aboard. A body is washed up on a Sydney beach, which also raises Cato's suspicions that there is a impostor on board the boat. When the boat's radio is smashed the crew are unable to receive further information. Then, when the drinking water tank is sabotaged, they are forced to stop off at an Indonesian island to get more drinking water.
—jem