In Singapore Harbor, 1883, the Batavia Queen stands in the early morning light beside a carelessly strewn dock. Aboard the ship is Captain Chris Hanson (Schell) who stands waiting for his passengers to arrive. The first to board is a slim, intent woman. Her name, Laura (Diane Baker). The Captain assures her that the rest of the passengers will be arriving shortly and she disappears.
As the ship is loaded with merchandise and a strange tear-shaped metal diving bell, the others begin to come aboard. First to arrive are a slim, blond woman and a drunken broad-shouldered man, They are Charley (Barbara Werle) and Connerly (Brian Keith). She is an out-of-work nightclub singer in love with the rough, so self-confident Connerly, a diver and explosives expert, at home int he roughest corners of the world.
As a scientist Douglas Rigby (John Leyton) supervises the loading of his Diving Bell, he sees the boarding of Giovanni and Leoncavallo Borghese (Rossano Brazzi and Sal Mineo). Between this father and son there is little love. They are adventurers - balloonists who have sunk to carnival-act level - but who retain their pride.
Soon the ship is boarded by an officer who orders the captain to transport some 30 prisoners to the island of Madura. Hanson points out that his destination is Krakatoa, but makes no impression on the officer, who brings the men in irons aboard the ship under armed guard and herds them into a hold. Once the ship is underway with First Officer Jacobs (Mark Lawrence) and helmsman Jan (Alan Hoskins) at the wheel, the purpose of the mission is made clear. Some years before, Laura's husband, a ship's captain, was lost with his ship off the coast of Krakatoa. Laura has talked Hanson - her late husband's rival for her love - into a salvage operation. She claims that there is a fortune hidden above the sunken ship.
The next morning Leoncavallo makes the pleasant discovery that there are four lovely Japanese diving girls aboard the Batavia Queen. Led by Toshi (Jacqui Chan), they are to aid in the search for the lost ship for an equal share in the treasure. As Leoncavallo makes their acquaintance, Hanson and Laura explore their past, and with delicate insistence, Hanson pulls from her the admission that she had never loved her husband, but that the shock that had sent her into a nervous breakdown had been the loss of her four-year old son where husband's ship sank. Having known one of the prisoners in the past, Hanson allows Danzig (J.D. Cannon) the freedom of the deck and as they sail towards Krakatoa, tensions mount. A high pitched, maddening penetrating noise cuts through the night. Lights of an unexplainable beauty are seen on the horizon. In the oppressive, strange and unfamiliar weather, Connerly hides himself away with a bottle and, in his drunkenness, attacks one of the Japanese girls. His punishment comes the next day. Hanson has him strung aloft in a cage, where in the heat and motion of the ship, he raves of his revenge.
The ship lumbers on through an impenetrable haze, until at last the mysterious fog lifts and Krakatoa is revealed in the distance. Soon the balloon is sent aloft, piloted by Leoncavallo. For days they follow it, searching for the sunken hull of the lost ship. No sooner is the hull finally located than the balloon is sucked into the powerful updraft emanating from the rumbling volcano. It catches fire, but the Borghese are saved after leaping into the sea.
Connerly dives below to investigate the wreck and his life is almost lost in the explosion that frees the safe from the sunken ship. In the excitement the prisoners aboard the ship, led by Danzig, surprise and overpower their guards. Hanson is forced to dive below to aid in bringing the safe to the surface. He finds a weapon that eventually allows him to overcome the freed prisoners. Danzig dies at the Captain's hand, and rest of the prisoners are abandoned to the sea in a lifeboat.
The safe is discovered to contain no treasure, but Laura is not upset. As the rest of the team threaten her, she points out that the log book indicates where the treasure - a dispatch box, loaded with pearls - is located. With the log in their hands, they sail for Pelambang Point, under the increasingly active, threatening explosions of the volcano. During the perilous passage to Pelambang Point, fireballs fall from the sky, the ship is buffeted by explosions, and steaming lava falls into the heaving sea. The sails catch fire in the wild melee.
It is during this passage, too, that Laura explains to Hanson her mission. It is not the pearls she is after. An entry she tore from the log tells her that her husband has left her son at the mission at Pelambang Point. It is her son she is seeking and nothing will stop her. The battered ship finally reaches the mission only to find it abandoned. They learn that the priests and all members of the mission have fled. The Batavia Queen sights a floundering Sampan. It is in danger of sinking, and the crewmen of the Batavia Queen leap into the sea to save the children aboard it. Among those saved is Laura's son Peter and he is soon engulfed in his mothers' arms. The strong box with him is grabbed by the members of the crew and when opened is discovered to be filled with an unbelievable collection of pearls. The treasure is divided into equal shares and at that moment the tortured volcano of Krakatoa disappears in the largest explosion the earth has ever known.
Panicked by the unbelievable explosion, some of those aboard the ships set out in a small boat for a nearby island. But Hanson, trusting to his ship, steams for the open sea in the hope of escaping the worst of the giant tidal wave he knows must follow the cataclysmic disappearance of Krakatoa. In the final scenes, the Batavia Queen plows into the open sea. The tidal wave strikes the island, leaving it bare. And the ship and those left aboard it prepare to meet the most enormous challenge of their lives, alone in the open sea."Photo Gallery