Gasu ningen dai 1 gô
A high-speed pursuit between police and an escaping robber along Itsukaichi Highway is under way. The pursued car crashes and overturns down an embankment. Two policemen and Detective Okamoto (Tatsuya Mihashi) look to find the robber and are astonished to find nothing inside, not even blood.
The men hear the strains of music outside the property of a large nearby house. Okamoto directs one of the men to search the premises, while the other rings the buzzer at the front door. Investigating the music, Okamoto sees an outdoor stage upon which a dancer wearing a grotesque mask is rehearsing, accompanied by her servant Jiya. As the dancer ends her routine, the buzzer sounds. Jiya answers the door and informs the officer that he and his lady, Fujichiyo Kasuga (Kaoru Yachigusa), are alone and nobody has been by. The cop tries to take a peek inside, as Jiya informs him they do not have a car.
The next day, Okamoto shares lunch with his girlfriend, newspaper reporter Kyoko Kono (Keiko Sata). Kyoko questions him about the details of the robbery. Okamoto reveals there are no clues on how it was done or who did it. Kyoko feels she can find out as much information as Okamoto can, and perhaps even solve the case. Okamoto doesn't take her seriously.
The police officer who earlier had driven the squad cars is thanked by the bank president for supplying extra guards. The bank president assures the cop that the bank's alarm is tested every day. The alarm suddenly goes off as a mysterious robber kills a bank employee and confronts the police officer. The cop opens fire on him, but the bullets have no effect on the robber. More cops from police headquarters arrive. They observe the dead employee behind the locked bars that protect the safe. The bank president, overwhelmed with grief, is led away.
At a meeting with the editor, lead employee Kawasaki (Kozo Nomura) suggests that Kyoko try to get information out of her boyfriend. Although she doubts Okamoto would keep any new developments from her, she gets a call from him inviting her to lunch. They meet, and Okamoto asks Kyoko if she has ever heard of the dancer Fujichiyo. She can't give much information, other than that the dancer comes from a distinguished family and was at one time wealthy, but has not danced in some time. Okamoto wonders why, and Kyoko tells him it's because of the dancer's parents and grandparents, but he doesn't believe her. Sensing trouble, Kyoko leaves the restaurant and calls her newspaper for more information on Fujichiyo.
Okamoto's boss Tabata (Yoshifumi Tajima) informs him of the bank robbery and that an employee and a policeman have both died of suffocation by the mysterious robber. There are still no clues as to who did it. Okamoto tells his theory that the dancer Fujichiyo might be behind the robberies, but Tabata does not believe him.
The next day, Okamoto heads to Fujichiyo's house without official permission. Kyoko drives up and offers him a ride, but he lectures her and she drives off. Kyoko arrives at the dancer's house and sees a brand new car being dusted by a chauffeur. She meets Fujichiyo and discovers that she will give a solo recital in a month, with a supporting company, and she requests that no word be given out yet, as things are not definite. Kyoko points out that the publicity would be helpful. The dancer insists that nothing official be released yet, and that there is no guarantee that any announcement will be made if and when the recital does take place.
As the car carrying Fujichiyo travels down the road, it passes Okamoto. Kyoko drives up and lets him get in and they follow her. They find her at a public library and see her check out a book. The librarian Mizuno (Yoshio Tsuchiya) tells them the book she checked out contained ancient songs, and that she studies the library's ancient engravings.
Fujichiyo leaves and stops at the home of a respected chamber music tutor named Osaki (Kamayuki Tsubono). He informs her that he is too busy training to assist her at present. She then offers him 200,000 yen if he will perform. Osaki is amazed at the amount and gladly takes it.
Upon returning to his office, Okamoto discusses his research into Fujichiyo's affairs with his boss and her plans to stage a comeback. He believes she is getting the money from an unknown sponsor. Tabata suggests Okamoto continue his investigation.
Kyoko's newspaper office receives a call from a man claiming to be the bank robber, demanding to speak with the editor. The man states that at 3:00 the next day, he will rob the Kyodo bank in Shhinjuku. He suggests the bank employees be given prior warning so no one will get hurt. The man hangs up before insisting they make sure the story is printed correctly.
The next day the Kyono bank is infiltrated with police posing as bank employees, waiting for the robbery attempt. Some are positioned inside the vault. The hour of 3:00 is announced by the clock. A policeman named Hotta (Yukihiko Godo) tells Okamoto the time and that the robbery should have occurred by now. However, Inspector Inao (Yoshio Kosugi) comes inside the vault to tell them that they have caught the thief attempting to rob the bank. The captured man (Rem Yamamoto) is interrogated by the police and he tells him that he is the one who issued the warning on the phone. The police demand to know where the 56 million yen ended up, but he doesn’t know where the money is.
Okamoto and Kyoko meet at a restaurant where she congratulates him, but he doesn't believe the man's story, and still feels the answer lies with Fujichiyo. Kyoko admits the man's arrest does not answer the question of how the dancer got the money. She reasons that she might have gotten it from her family. Another detective enters the restaurant and tells Okamoto he is needed back at HQ. At police headquarters, Tabata announces that a theater hired for the recital has received money with serial numbers matching those of the stolen money. The police arrive at Fujichiyo's house and search the premises. Okamoto finds the money, and the serial numbers match. She is taken to police headquarters and questioned by Okamoto and Inao. They ask who gave her the money, but she refuses to tell them.
Some time later, the librarian Mizumo enters the police headquarters, where a group of journalists are in the Press Room. He then tells them that he was the one who robbed the banks to get Fujichiyo the money, but they are skeptical. He leaves and enters the conference room of the police station. Okamoto recognizes him and Mizuno offers to show the police the method used, on the condition they take him to the site of the second burglary. He is brought to the bank, where the circumstances will be recreated, with the bank president playing the part of the deceased employee. Mizuno walks up to the bars and to everybody's surprise he transforms himself into a cloud of swirling vapor in front of everybody. The police fire at him, but the bullets have no effect. He then goes though the bars and suffocates the bank president, killing him. The Gas Man then opens the bars and takes a stack of money. Inao fires several bullets at the Gas Man, with no effect. The Gas Man throws the money at Inao's face and wraps around the man's neck, killing him. The gaseous form of Mizuno escapes though an overhead window before telling the police that Fujichiyo is not guilty and they must release her from custody.
A meeting is held in police headquarters. Fujichiyo still refuses to cooperate with them capturing Mizuno. They keep her in custody so that they have a chance of catching Mizuno. However, Mizuno appears suddenly on the room and the police try to catch him. Okamoto shoots him at point-blank range but he escapes in his gaseous form.
Mizuno then heads to the prison where Fujichiyo is being held. He kills two policemen and unlocks the dancer's cell. Fujichiyo tells him that if she escapes with him she will be considered a criminal. Mizuno insists she comes with him, but she still refuses. He listens to her, releases all of the prisoners and vanishes. A riot erupts between police and prisoners. While all of this is happening, Fujichiyo sits quietly in her cell alone.
In the newspaper office, Kyoko gets an idea of how to further his cause for Fujichiyo's freedom. She suggests contacting the Gas Man to her editor for an interview. The newspaper prints an invitation to him and an impromptu meeting is set up on the upper floors of an office building. The interview begins with Mizuno assuring the press that he is not from outer space, but is an earthling as they are. He is asked how he became the Gas Man. Mizuno brings up the late professor of biology, Dr. Sano (Fuyuki Murakami).
His story begins as he was working at a college library. His successful career as a test pilot in Japan's Self Defense Force was cut short, due to the discovery of cancer in his lungs. He was visited by Dr. Sano, a professor at Johoku University and a medical doctor of Japan's space research program. It turns out that Mizuno was referred to the doctor by the Self Defense Force because the training he received made him a perfect candidate for their space pilot Ppogram. Dr. Sano said that they were going to change the existence of the human body, which would allow it to withstand the intense heat of the sun. Mizuno was offered 20,000 yen to undergo the experiment, but he admits the money was not important to him. He went to Dr. Sano's lab, where he was given an injection and lay down on a metal table where he is secured by steel bars. Dr. Sano turned on the machine and Mizuno soon fell asleep. Later Dr. Sano opened the chamber to find that Mizuno had become the Gas Man, with swirling mist where his body once was. Mizuno then regained his former shape with ease. He accused the doctor of deceiving him as to the true purpose of the experiment. Dr. Sano tried to leave but Mizuno caught him. Dr. Sano accidentally reveals that Mizuno was not the first person he experimented on. Realizing that the doctor might have killed them, and feeling betrayed, Mizuno kills Dr. Sano.
Resuming his interviews, Mizuno admits that he feels indebted to the doctor. Because of his new-found powers, he can help Fujichiyo dance again. He also admits that he loved her before he became the Gas Man. The police suddenly barge in and fire rifle grenades loaded with poison gas, but to no avail, as Mizuno escapes again.
The police ask Fujichiyo to help them catch Mizuno. A Dr. Tamiya (Hisaya Ito) patronizes her, and says that he does not believe she knowingly received stolen money. Feeling the Gas Man is a threat to society, he and the other officials ask that she help them set a trap for him at her concert. She does not go along with the plan. The police have no choice but to set Fujichiyo free.
In the newspaper office, it is revealed that an unspecified tragedy had affected Fujichiyo's life, forcing her to live her current existence.
Fujichiyo meets Osaki and is told that the musicians are to scared to perform the concert, fearing a confrontation between the Gas Man and police. Fujichiyo tells him not to worry and that she can do the recital without them. Mizuno appears before her and he says that everything is ready for her recital, but he is upset that the money to make her recital was stolen, and upset at the taking of other people's lives. Mizuno is unperturbed by such trivialities. He tells her that what he did was all for her and that his love for her is an obsession.
Dr. Tamiya meets with Okamoto and Tabata at Dr. Sano's lab. They devise a plan how to do in the Gas Man without harming Fujichiyo. They decide to use U.M. gas which can be detonated in an enclosed area. The theater Mizuno chooses as the location for Fujichiyo is such a place.
Kyoko pleads with Fujichiyo to cancel the concert. The dancer resists the suggestion, seeing it as her destiny. Kyoko persists in her argument. Fujichiyo has been told by the police that they intend to trap Mizuno. In the process, many people may be inured or killed. Kyoko reckons the audience will be mostly thrill seekers, hoping to catch a glimpse of the Gas Man. She insists that Fujichiyo tell Mizuno not to attend, then help the police try to capture him later. Fujichiyo tells her that she must perform so that she can return the honor for his sake. Kyoko then asks her if she really loves him after all that has happened. Surprised at the question, Fujichiyo says that she does.
On the night of the recital, an unruly mob and a frenzied media gather outside the theater. The police try to keep both groups away from the theater. Fire engines are at the ready once the gas has been detonated. Kyoko manages to break though the police barricade and runs for the theater. Okamoto follows her in. As Kyoko enters, she sees Fujichiyo and Jiya on stage as the dancer performs "Daughter of Fuji". Mizuno is seen sitting in the crowd watching contentedly.
In Sano's lab, Tabata and Tamiya discuss the challenging task of trying to fill the theater with gas, getting everyone but Mizuno out, then setting the theater ablaze.
As the recital continues, the crowd begins to get restless, waiting for the Gas Man to appear. Mizuno stands up and informs them that he is the Gas Man, but the crowd is obdurate. Mizuno transforms into his gaseous state, scaring all but one from the theater. During the disturbance, Kyoko runs to the stage pleading with Fujichiyo to leave, but she refuses to stop, saying that this is her final performance. Her servant also insists on staying with her. Mizuno alerts Okamoto to the fallen man.
At the lab Tamiya suggests to Tabata that they wait until Mizuno is completely alone in the theater. Tabata is torn for he doesn't quite have the opportunity he needs to set fire to the place. Having no choice, he orders the gas to be released.
Okamoto and Kyoko take the fallen man out of the theater. They head for Sano's lab with news that Fujichiyo and Jiya have insisted on remaining with Mizuno. Tabata decides to throw the switch but Kyoko pleads with him not to do it. Tabata says it is too late to stop now. The switch is thrown but nothing happens. They find out that the detonating wires on the circuit board have been severed by Fujichiyo. As the recital ends, Fujichiyo bounds off the stage, embracing Mizuno. While savoring the moment with the man she loves, she reaches for a cigarette lighter to burn the theater down along with Mizuno and Jiya. Knowing that they can never live happily together as a normal couple, she ignites the lighter, causing the theater to go up in a maelstrom of flame, killing Fujichiyo and Jiya.
While everyone outside gazes at the burning theater, they wonder if the Gas Man is dead. They then see the mangled, smoldering clothes of the Gas Man, slowly crawling out of the theater then returning to his original form, dead.
insanity, murder