United World News reporter Steve Martin awakes in the rubble of a devastated Tokyo. Hours later, rescue workers remove him to a hospital overflowing with the injured and the dying. Martin is soon found by an old friend, Emiko Yamane, who is assisting at the emergency hospital. Steve Martin reflects on how it all began...

While Steve Martin is flying to Cairo with a lay over in Tokyo, thousands of feet below an incident occurs in the Sea of Japan. A Japanese fishing ship is destroyed by a mysterious flash of light from beneath the sea. Japanese officials question all of the airline passengers when the plane lands in case they saw anything that relates to the disaster. Martin soon makes the acquaintance of Officer Iwanaga. The Japanese official tells the reporter what little is known. Martin is intrigued and accompanies Iwanaga to the office of the Nankai Steamship Company, whose ship it was that sank. The company is at a loss to explain the sinking. By radio, they are in contact with a rescue ship which is rapidly nearing the area of the sinking. All are shocked when the rescue ship meets the same fate, just as mysteriously. The news spreads like wildfire. Soon, eight ships have been claimed by the unseen force and all shipping is banned from the area. What few survivors are found die soon after rescue from shock and strange burns. With such a story happening in Tokyo, the Cairo leg of Martin's trip is cancelled.

Scientists and officials meet to decide how to deal with these ship disasters. Among them is Dr. Yamane, Japan's premier paleontologist. He suggests an investigation be sent to Odo Island, which lies in the region of the ship disasters.

On Odo Island, a survivor of the sinkings washes ashore. Like the others, he dies minutes after the islanders find him. The next morning, a helicopter from Tokyo arrives, bringing investigators to question the natives. Officer Iwanaga arranges for Steve Martin to join the investigation. They discover that the natives think that a monster is responsible. A twilight performance of an ancient ritual gives the investigators the monster's name - Godzilla.

That night, a tropical storm strikes Odo Island. Sensing danger, young Shinkichi flees his home during the fierce gale. His parents remain and perish when the dwelling collapses about them. Over the fury of the storm, a thunderous shriek sounds. Shinkichi screams that Godzilla is attacking the village. Even Steve Martin is convinced that something more than wind and rain has visited Odo Island.

Some of the islanders are brought back to Tokyo to make an official report. Although the tales of Godzilla are ridiculed, it is decided to send a better-equipped team to the island. Dr. Yamane will head this expedition. Steve Martin receives Yamane's permission to join the expedition. Yamane's daughter Emiko joins her father as well. Although formally engaged to Dr. Serizawa since both were small children, Emiko soon falls in love with a sailor named Ogata.

The ship safely plies the dangerous waters and arrives at Odo Island. Dr. Yamane examines massive footprints in the ruined village, discovering a living trilobite inside one. The prints are also discovered to be radioactive. Soon, the village's alarm bell sounds. Villagers and investigators alike flee into the hills. Their flight is brought to a halt when a monstrous reptilian head peers over the hill. Godzilla roars at the cowering people before slipping out of view behind the hill. He leaves behind him massive footprints which lead into the sea.

Back in Tokyo, Dr. Yamane makes his report. Godzilla, he says, is a prehistoric creature brought back to life by atomic radiation, specifically H-bomb tests. The Japanese decide to destroy the monster. Cruisers are sent out, employing depth bombs to kill the submerged monster. Meanwhile, Steve Martin calls his old friend Dr. Serizawa. Serizawa begs off meeting with his friend, as he is meeting with Emiko later that afternoon. Serizawa prevents Emiko from telling him about Ogata when he shows her the results of his experiments. Serizawa makes his fiance swear to tell no one of what he has shown her.

Believing Godzilla to be dead, Tokyo breaks out in a great celebration. Only Dr. Yamane seems upset, believing Godzilla should be studied, not destroyed. The celebration is short-lived when Godzilla appears in Tokyo Bay. News of Godzilla's appearance plunges the city into panic and the military is deployed. The next evening sirens announce Godzilla's return. The monster attacks Tokyo's railyards, crushing trains with his powerful jaws. Steve Martin and Dr. Yamane join the masses of on-lookers. At last, Godzilla returns to the Bay. Dr. Yamane grimly predicts that he will be back.

The Japanese decide that they will try to stop Godzilla with a fence of high-tension electrical towers. This will keep Godzilla out of the city's heart. Even so, Tokyo's evacuation is begun. By nightfall, the streets are quiet. From the news office, Martin and other reporters await coming events. Martin decides to make a tape-recording of his report as events unfold in case he does not survive.

All to soon, Godzilla emerges from the Bay. Howitzers blast the beast, to no effect. Godzilla makes his way to the electric fence. The barrier also has no effect on him, and Godzilla soon breaks through, employing his atomic breath to melt the metal structures. Godzilla proceeds into the city, igniting whole blocks with his fire. The monster's rampage is unrelenting and unstoppable. An entire tank core is moved to point-blank range, but their shells are utterly useless on the monster. A single blast of Godzilla's fire breath reduces them to smoldering wrecks. Tokyo burns as Godzilla's onslaught continues. The heart of Tokyo is nothing more than a sea of fire.

The flashes of cameras from reporters on Tokyo Tower causes Godzilla to attack the structure, pitching the unfortunate men to their deaths. Godzilla's path of carnage brings him toward the news office. Realizing escape is impossible, Steve Martin continues to report into his recorder even as the building collapses around him.

The fiery holocaust continues and Godzilla moves back toward the Bay. Finally, jets arrive, their missile fire aggravating Godzilla and finally driving him back into the sea. Again, everyone is certain that it is only a short reprieve.

In the emergency hospital, Martin talks to Emiko and Ogata. Emiko reveals to the two men that she knows of a weapon that will kill Godzilla. She breaks her oath and reveals the experiment Dr. Serizawa showed her - the oxygen destroyer. A pellet-like device, when placed in water, it removes all oxygen, disintegrating all living matter. Serizawa is worried that his discovery might be used for evil and made Emiko swear to secrecy. With the threat of Godzilla hovering over Japan, Emiko and Ogata decide to see Serizawa and get the weapon.

At Serizawa's, Ogata reveals that he knows about the oxygen destroyer. Serizawa refuses to give up the weapon. Desperate, Ogata struggles with the man in his lab. Serizawa bests Ogata in the melee but notes how Emiko treats the sailor's wounds. Serizawa states again that he fears the oxygen destroyer will fall into the wrong hands. Ogata tells him that he has a terrible decision - his fear, which may become reality, or Godzilla, which is reality. Serizawa agonizes over his dilemma, at last conceding, but insisting it must be the only time it is used. The scientist proceeds to burn all of his research.

Soon, a cruiser makes its way to the middle of Tokyo Bay, using Geiger readings to locate Godzilla. While Emiko, Dr. Yamane and Steve Martin watch, Serizawa and Ogata descend into the water wearing deep-sea diving suits. They soon see Godzilla advancing in their direction. Serizawa motions for Ogata to ascend while he deploys the oxygen destroyer. Ogata calls for Dr. Serizawa to hurry and follow him.

The oxygen destroyer soon does its terrible work, engulfing Godzilla in its destructive force. Serizawa waits until he is certain it is working. He tells Ogata and Emiko to be happy together. Ogata orders that Serizawa be pulled up, but it is too late, the scientist has cut his lifeline and air hose. The secret of the oxygen destroyer will die with him.

Godzilla surfaces, screaming his death cry. Sinking once again, the oxygen destroyer swiftly disintegrates even the monster's bones. As Steve Martin reports - Godzilla is dead, but at the cost of a great man.