In this book we meet once again Wandering Will, one of Ballantyne's perpetual heroes. They are on a touristic cruise in the eastern Pacific, when the second mate, Griffin, eggs on some of the seamen to mutiny and take over the ship. The captain and some of the senior officers are cast off in a ship's dinghy to survive however they can, while Will and others of his party are retained on board the Rover, because of their medical knowledge, which Griffin believes might one day come in useful.