A salvage boat's captain gets mixed up with island convicts during a volcanic eruption.

In 1883 the Batavia Queen leaves Singapore harbor. Her destination is the coast of volcanic island Krakatoa, where a ship laden with pearls has sunk. Among her passengers are Laura, widow of the lost ship's captain; Rigby, a claustrophobic diving bell pilot; the Borgheses, father and son balloonists; and Toshi, the leader of a team of Japanese diving girls. Also aboard are 30 prisoners, including the convict Danzig, who is given freedom of the deck. As the ship approaches Krakatoa, catastrophes occur in rapid succession, including accidents and natural disasters. Caught while aloft in the updraft of Krakatoa, the Borgheses save themselves by diving into the sea. Led by Danzig, the mutinous prisoners briefly control the ship. Captain Hanson retaliates by killing the convict and setting his fellows adrift in lifeboats. Upon recovering the sunken ship's safe, all are shocked to discover it empty, save for a log. Although Laura placates the passengers by assuring them that the diary specifies the treasure's location, she later reveals that she is searching for her son, left by her husband at a Catholic mission. When the Batavia Queen rescues the mission's staff from a sampan, the boy is among those saved. Presented by her son with the coveted pearls, Laura begins division of the treasure. However, Krakatoa erupts, causing a massive tidal wave. To escape certain destruction the ship takes to the open seas.