At the Ginza 4-chome, the dead body of an invisible man is discovered, alongside a suicide note. The note reveals that there is at least one other invisible man still alive. An ex army commander reveals that during the war, Dr. Nishizaki discovered by chance a particle that, when properly utilized, turns any object invisible. At the end of the Pacific War, a special attack corps made up of invisible men crashed on Saipan Island, and were presumed dead, however two survived. The effects of invisibility cannot be undone. Soon, there are robberies across down from a gang calling themselves invisible men. Meanwhile Nanjo, a clown who works at the cabaret Kurofune befriends a young blind girl, Mariko, who lives in the same apartment. Komatsu, a newspaper reporter who witnessed the death of the invisible man, is investigating the phenomenon, and spots Nanjo while visiting a robbed jewelry store. In a fake deal to gather money to cure Mariko's blindness, her grandfather is killed by the gang that has been terrorizing the town. Soon after, Komatsu, who has been following Nanjo, finds himself alone in a room with him, and discovers that Nanjo is, in fact, the other invisible man. He dresses as a clown with face makeup, gloves and so on so as to appear visible and lead a relatively normal life. Nanjo and Komatsu decide to work together to investigate and reveal the identity of the gang who is terrorizing the town and who murdered Mariko's grandfather, while also trying to save Michiyo, a singer who is stuck within the gang and cannot escape. They discover that the gang is lead by the same people who own Kurofune, and in an ensuing battle and chase, Nanjo, using his invisibility to his advantage, saves Michiyo and kills Yajima, the gang boss. However, he is also fatally wounded in the fight, and becomes visible again. He asks Michiyo to take good care of Mariko in his last breath.
The Invisible Avenger was distributed in Japan by Toho on December 29, 1954. Any release of the film in the United States is undetermined. Daiei Film produced two similar films featuring invisibility, Tomei ningen arawaru in 1949, and Tomei ningen to Hai-Otoko in 1957.
