Shipwrecked, Daisaku (Johnny Sokko) and Juro Minami (an agent forUnicorn) drift to an island and are captured by the BF gang. The island is in fact, a base of the B.F. gang. They happen to discover a huge robot while they are running away. Giant Robot is being constructed by Dr. Gartua who is aware of the wicked project to conquer the earth by the B.F. gang. Dr. Gartua explains that Giant Robot works by atomic energy and only obeys the person who gives the original order. When Dr. Gartua tries to destroy the robot, his lab is destroyed. From the ruins Giant Robot stands up. Daisaku speaks to it and it is decided that he is the one who can control it.

Emperor Guillotine, king of BF syndicate, plans to take back Giant Robot and to arrest Daisaku (Johhny Sokko), the only one that can give orders to the robot. He sends a huge magic metal globe called Glober to the earth. Then he orders Spider, head of the BF Japanese branch, to arrest the boy and the robot when they come to destroy it. The globe falls to the top of Mt. Makone and starts to roll down the mountain toward the town. The tank corps of the Defense Force attackit in vain and town people are thrown into confusion. Carrying a small rocket on his back, Daisaku comes flying to the town and calls Giant Robo.

Under Emperor Guillotine's orders, Dr. Over, a leading member of BF Syndicate, comes to the earth with a fossil of a devilish space plant called Satan Rose. He kidnaps Yasui, an old botantist. In the underground laboratory Over tells him to bring the seed of the plant back to life. As Yasui refuses, the doctor performs an operation on his brains. Now as Over's slave, Yasui obeys his orders. The fossil breaks into two and a small black bud starts to grow. Put in a building and destroys it. People are struck with terror and run about helter-skelter.

Emperor Guillotine sends Dr. Over and Ligon, a new weapon in the shape of a pyramid, to the earth. By operating Ligon, Over destroys oil fields in Araia one after another. The price of oil soars in all countries and the world economy is thrown into confusion. Then the doctor tells Hishino, a Japanese oil engineer in the Arabian Desert to help him. Hishino refuses, and he is imprisoned in Ligon together with Arabian members of Unicorn Organization. Suspecting that all the trouble was caused by BF Syndicate, the head of the Japanese Branch of Unicorn Organization sends two members -- Minami and Mitsuko, Hishino's sister -- to Arabia. On the way their plane explodes, but they are rescued by Daisaku (Johnny Sokko) and Giant Robo who have been following the plane.

A strange huge plant which has appeared suddenly in Sagami Lake sucks in all the water including a sailing boat and a man in it. Azuma, head of the Japanese Branch of Unicorn Organization, thinks that it must be Satan Rose, a space plant brought to the earth by Dr. Over. He sends Daisaku (Johnny Sokko) and Minami to the house of Yasui, an old authority on the plant. Meanwhile Over tells Red Cobra, new head of the Japanese Branch of the syndicate, to kill Yasui before he gives information about the plant to Unicorn members.

Dr. Over makes Ligon swallow a train near Lake Biwa to kidnap Suzuki, one of the passengers and head of the Kyoto Branch of Unicorn Organization. In the headquarters of BF Syndicate in the bottom of lake, Suzuki sees Over and Black Dia, new head of the Japanese Branch of the Syndicate. Azuma thinks that Over has killed Suzuki, for he is in charge of the conference of Unicorn leaders of the world which is going to be held in Kyoto. Under Azuma's orders, Daisaku (Johnny Sokko) and Minami go to Kyoto carrying the important papers concerning the conference. Over and Black Dia try to steal the papers, but they fail. Over changes Suzuki into a cyborg by performing an operation on him.

A monster called Dorogon swallows a jet plane of the Commonwealth of Sordia when it is flying and an atomic submarine of Furenkov Republic when it is under the sea. Without knowing the truth, the President of Sordia and the Premier of Furenkov lay the blame on each other. It was Emperor's Guillotine's plot to make the two countries fight and to enlarge it into a world war. The leaders of the Unicorn branches all over the world decide to have a secret conference to make peace between the two countries. Disgusing himself as head of Canada branch, Spider goes to the place of the conference, a villa on an uninhabited island, with his men and a bag containing a time bomb. In the garden of the villa, Daisaku (Johnny Sokko) overhears Spider's men talking and with the help of Giant Robo set out to stop them.

Dr. Tadokora develops QQV, a super-excellent transparent metal. He tests it and QQV endures all the attacks of Giant Robot. BF gang watch the experiments using TV cameras and try to rob the specifications of QQV. BF agents disguise themselves as Unicorn agents and sneak into the lab where the secrets are hidden. They succeed and rob an attache case but are pursued by Juro and Daisaku (JohnnySokko). The BF gang orders Gunger to attack Juro and Daisaku who also mobilize Giant Robot to counter attack.

There is the decoding office of the Japanese Branch of Unicorn Organization in the basement of a lighthouse on the coast of the Pacific Ocean. One night, the lighthouse is attacked by a monster that has come out of the sea and all the members are killed. Receiving an SOS, Daisaku (Johnny Sokko) and Minami rush to the scene. The building has become a ruin and the decoding machine is gone. It is serious, for if it falls in the hands of BF members, the secret places of Unicorn branches all over the world will be found out. They don't know that Spider and his men are hiding with the machine in a cargo boat on a nearby pier.

Daisaku and Minami happen to help a one-eyes man BF members are chasing. According to the man's story, they are trying to kill him as a traitor because he became frightened by the inhumanity of the syndicate and quit it. After taken to Azuma's headquaters, the man tells him that three children have been imprisoned by BF members in their secret base in a cave at the foot of a mountain. Daisaku and Minami rush to the scene with the man as their guide. They enter the cave and find the children, but they are startled to hear that a two-faced monster engraved on a rock is alive. When they are trying to run out, the one-eyed man points a gun at them. He turns out to be Black Dia, new head of the Japanese branch of the syndicate. They realize they have fallen into his trap, but it is too late.

Emperor Guillotine gives Dr. Over a spaceship equipped with all kinds of scientific weapons. After landing at the earth, Over sends an electric monster called Sparky to the ground of a soccer game and kidnaps all 30,000 spectators as hostages. Then Black Dia announces that he will be killed if Giant Robo takes action. Daisaku puts a small radio in Over's car to locate their headquarters. Over finds it and is exasperated. He tells them that he will have Sparky destroy the whole city of Tokyo unless the Japanese Government surrenders unconditionally by next day's noon.

Unicorn members locate the secret headquarters of the Japanese Branch of BF Syndicate. They attack the house and arrest Dr. Over by taking his blue star-shaped metal on his chest, the source of his magical power. Daisaku leaves the metal with Marie, a young girl who has lately joined the organization. After having a narrow escape, Black Dia is told by Emperor Guillotine to take back Over by using Unabalan, a synthetic monster. Next day, Azuma is asked to investigatea strange case in Uano zoo. A python dies and a hard substance like a fossil is found in its belly. And all the snakes in the zoo are found dead. Azuma brings the substance to the headquarters and puts it in the medical room. That night, it turns into a dreadful monster and helps out Over from the prison by killing a guard.

The underground office of the South Pole Unicorn Branch is buried in red sand which suddenly started to gush out in the ice field. As the communications are cut off, Azuma sends Daisaku and Ninami there to see what happened. Before their departure, Marie gives her pendant to Daisaku as a talisman. In the South Pole all the office members are found dead. When two men are gazing at their bodies, red sand starts to flow from the hatch. They soon notice it, but it is too late.

One day, a huge ball of fire appears in the space and blasts the communications satellite of Unicorn Organization. To investigate the course of the accident, Azuma sends Giant Robo to space. When the robot tries to catch the ball, it explodes and Glober, a huge magic globe, appears. It emits strange rays at the robot, making it stop spouting the jet stream. Then it catches Giant Robo with its long three legs. They fall down to earth and fall into sea. Daisaku and Minani leave by helicopter to search for the robot. When it is flying on a small island near Izu Peninsula, Daisaku's locator reacts to the transmitter he has set in the robot. Red Cobra and his men who have occupied the island shoot missiles at the helicopter. It explodes and disappears.

There is a small quiet Allah Republic at the foot of the Alps. The only product of this beautiful country is gold. Her peace is broken when a vein of new ores is found in a gold mine. It turns out to be dreadful Miracle Ion whose energy can melt the earth. King Allah receives a letter from Emperor Guillotine in which he demands MiracleIon. Unicorn Branch in the country ask the help of the Japanese Branch. Arriving there, Daisaku and Minani learn that Black Dia and his men have sneaked into the country although Miracle Ion is under the guard of Unicorn members. When they see Princess Sasal, king's granddaughter and only family, they are surprised at her resemblance to Marie.

The office of Unicorn Chinese Branch is attacked by tank corps led by Red Cobra. Chang, its head, asks the help of the Japanese Branch. Azuma, Daisaku and Minami fly there on Giant Robo's back. The robot destroys the tank corps at once and Red Cobra is arrested. Asuma and Chang leave for New York by helicopter to take the prisoners to the headquarters, and Daisaku and Minami return to Japan with the robot. On their way, the helicopter is swallowed by Iron Power, enemy's new weapon with huge iron teeth. Azuma and Chang are taken to a secret base of the syndicate in the heart of Mt. Izu. Azuma, however, succeeds in communicating with the branch by a transmitter he has put in his shoe.

Daisaku and Minami suspect that a strange villa standing in the heart of the Japanese Alps is a secret base of BF Syndicate. They approach the house to get some proof, when men in the house notice them and look for them. When the two men get into danger, a mysterious man who calls himself Yanagida helps them and takes them into his hut. Although he isn't their enemy, he seems to have some grudge against the three men. During the fight it suddenly starts to snow. It is caused by Iceler, a huge icing monster of the syndicate. Daisaku calls Giant Robo, but the robot is frozen by Iceler's fluid and buried under the snow. Minami is arrested and Daisaku enters the house against Yanagida's advice to fulfill his duty as a Unicorn member.

One night a huge balloon comes down in the Ginza and lifts away a big building. Azuma who rushes there receives a challenge letter from a man who calls himself X7. Nothing has been known about X7, except that X7 is a very good spy of BF Syndicate. Next day, a boy called Kuredajoins Daisaku's class in school. He invites Daisaku and two boys into his house where he is living with his uncle after his parents died. Following them, Minami inhales poison gas in a taxi and faints. In Kureda's house all the children including Kureda faint likewise. By Ippei, Kureda's uncle, and Red Cobra, they are taken to the basement where Minami is imprisoned. Ippei seems to be X7 himself. Kureda asks their forgiveness saying that he didn't know his uncle was such a dreadful spy.

Red fluid is poured into the water tank towering over rows of apartment houses. People living there drink the water, writhe with pain, and become motionless. Newspaper headlines say "Residents of Apartment Town Victims of Mummifying Water". The members of the Japan Branch of Unicorn receive a taoe from the Mummy Man of the BF clan. The taped words threaten that unless Unicorn surrenders its Giant Robo to the BF within 24 hours, the entire population of Tokyo would be mummified. Just then the Unicorn radar satellite catches a shining object plummeting down to earth, aimed somewhere north of Tokyo.

Giant Robo is invincible. Flashes show its past deeds: slaying of Licon, the phantom beast, shattering to pieces the super-robot beast Unbalan, the last sputterig of space plant Santalaws, etc. The Japanese government is asked by the Republic of Merea, the largest power of the world, to reveal the secret of Giant Robo's brain. The fact that Japan has the most powerful robot in the world is embarrassing to the people of Merea, the nation which surpasses every other nation in everything except robot-technology. Japan is on friendly terms with Merea, and the government authorities decide to do as proposed. The news reaches the Japan branch of Unicorn as the middle of the Giant Robo's birthday party and the party is ruined.

Beginning with the Swiss Branch, the Unicorn branch headquarters are mysteriously destroyed one after another. Rome, Cairo, Bombay, Singapore, Hong Kong, then Tapai. It is easy to guess that Tokyo will be next. Invariably, communication stops before a headquarter is destroyed, meaning that the radar post is attacked first. The Japan Unicorn men send two men to guard its radar post built on top of a mountain.

A saucer-shaped spaceship approaches Earth, and heads for Tokyo. It lands on a forested hill not very far from the city. But it is discovered lying harmlessly awkward. Two Unicorn men enter the hatch, and find a creature beamed down on the floor under the fallen control panel. They drag out the creature. It is no human being. It has three eyes. The creature is grateful for being rescued, and offers the men small pills which it claims is space food that would support a man without food for a year. But as soon as they take the pills, they fall stiffened like stone.

Tokyo's night sky is hit with flood of headlights flowing through the veins of elevated speedways. But below, the ground is dark and gloomy. From a manhole, a large blotch of black liquid oozes out and starts climbing one of the giant pillars supporting the speedway. Where it touches, the steel rots and softens like a sponge. The speedway crashes down, cars tumble in heaps and burn. The black ooze is Hydrozoon, the micro bean monster that eats up metal. Skyscrapers and towers crumble down. Tokyo is in turmoil.

U7, member of Japan Branch of Unicorn, is the one who controls the gigantic Giant Robo with the wrist-watch controller microphone. One day, he receives from his father a parcel as a birthday gift. It is a kit for constructing a man-size robot. But the actual sender of the gift is Professor Gurama whose home is a 4th dimensional nebula. The robot is completed. And, when U7 puts the switch in to animate it, a sudden change comes over the robot. There is, facing U7, another U7, exactly the same self to the last detail. The new U7 grabs the control wrist-watch. Just then, other members of the Unicorn come to see U7, and find two U7s, each claiming that he is the real U7.

U13, member of the Japan Branch of Unicorn, is on night patrol. At the entrance of a town he picks up a girl who is half frantic with fright. The girl explains that all the people of the town are dead. So it is. The street is littered with corpses. He shouts but there is no response. A door opens. He enters thinking that someone should be inside alive. He finds an old man who introduces himself as a vampire. U13 tries to run away, but his escape is blocked by the girl he had left in the car. The girl now has the vampire look.