Sir Geoffrey Radcliffe (Vincent Price) is sentenced to death for the murder of his brother Michael, a crime he did not commit. Dr. Frank Griffin, the brother of the original invisible man, injects the prisoner with an invisibility drug. As Radcliffe's execution nears, he suddenly vanishes from his cell. Detective Sampson (Cecil Kellaway) from the Scotland Yard guesses the truth while Radcliffe searches for the real murderer before the drug causes him to go insane.