Experimenting on making guinea pigs invisible by lowering their refractive index to that of air, Dr. Peter Brady becomes invisible himself after a radioactive leak. Brady becomes an official secret and seeks help from fellow scientist, Crompton, to make him visible again. But Crompton sees the advantages of invisibility and steals Brady's notes.
A British agent is held in a Middle East hospital by the secret police and Brady is asked to get him out.
Tricked into visiting the hideously disfigured Raphael Constantine who wants to become invisible, Brady is asked to recover a secret document which incriminates Constantine in a crime he claims he did not commit.
Tania, a Russian scientist working in London, criticises her government and is abducted. Brady comes to her aid, believing she can help him to become visible again.
One of Sally's friends is afraid her mother is going to be murdered by her stepfather and his sister, and Sally asks her Uncle Peter to use his invisibility to save her.
Brady tries to prove actress Barbara Crane did not accidentally run down and kill a tramp – for which she is being blackmailed – when even she believes she did.
Brady goes aboard an Iron Curtain ship in the London docks to rescue a prisoner, but discovers it is a trap using a form of radar to catch him and his secret of invisibility.
Unknown to puppeteer Penny Page, the mink coat she is wearing on a plane to Paris contains smuggled microfilm of atomic research papers. Fellow passenger Peter Brady becomes involved in the intrigue.
When Brady's friend is accused of drug smuggling and is nearly killed by the gang responsible in front of his blind wife, he becomes the woman's eyes to break the smuggling ring.
Convinced Joe Green, who has been convicted of armed robbery, is innocent, Brady searches for a girl who can provide an alibi.
When Sally is taken from school by a gang of ruthless criminals, Brady is forced to rob a bank to pay a £50,000 ransom for her safe return.
To save the daughter of Professor Owens, a brilliant scientist, from danger, Brady uses his invisibility to manipulate the casino tables in Italy in Owens's favour. But little does Owens know that he is gambling his daughter's life away.
After his bag of scientific documents is stolen, Brady is held prisoner by the man responsible, who wants him to commit a murder. The Invisible Man discovers that although his invisibility is a defence against detection from humans, it is no protection against a vicious guard dog trained to hunt him down if he attempts to escape.