Sir Geoffrey Radcliffe, Vincent Price, is sentenced to death for the murder of his brother Michael, a crime he did not commit. As his appeal drags on, his best ally, Dr Frank Griffin, John Sutton, and Geoffrey’s fiancée Helen Manson, Nan Grey, hatch a perilous plan to inject him with an invisibility drug if the appeal fails. The plan is set in motion, but it falters when the appeal is denied, and as the execution draws near, Geoffrey mysteriously vanishes from his cell just after Dr Griffin has visited him. The new case catches the eye of Detective Sampson, Cecil Kellaway from Scotland Yard, who recognizes the echoes of the famous invisible-man enigma and grows intent on uncovering the truth.
Dr Griffin has arranged a new identity and a way to keep Geoffrey safe, leaving clothes for him at a pre-arranged place while Helen hides him in a secluded cottage in the woods. Geoffrey begins a quiet, haunted search for the real murderer, all while the drug’s effects threaten to push him toward a madness that mirrors the original invisible man’s fate. Dr Griffin, meanwhile, pursues a cure, hoping to reverse the transformation and restore Geoffrey to sanity. Geoffrey’s plea to Griffin—if signs of madness appear, to stop him from harming others—binds the two men in a tense, uneasy alliance, even as the doctor wrestles with the limits of science and conscience.
The Radcliffe mining operation adds another layer of tension: Willie Spears, Alan Napier, a recently hired worker, is suddenly promoted, arousing Geoffrey’s suspicions about foul play within the company. In a confrontation that shakes the factory’s corridors, Spears is coerced into revealing that Richard Cobb, Cedric Hardwicke, Geoffrey’s cousin, is the man responsible for the crime. Yet the drama grows darker as Griffin and Helen observe clear signs that the invisibility drug is harming Geoffrey. In a desperate move, they secretly drug him to induce sleep, hoping the rest will restore his mind; on waking, the effect seems to have been only temporary, but the possibility of a staged recovery lingers.
Geoffrey escapes his confinement and presses on toward Cobb, intent on confrontation and truth. A dangerous pursuit ensues, culminating in a tense chase where Sampson fires a shot that wounds Geoffrey. Cobb’s end comes when he is fatally injured by a fall from a coal wagon, but not before he confesses to the murder. With the immediate danger behind him, Geoffrey receives devastating news: he is dying from blood loss and exposure. In a last, unyielding push toward life, Geoffrey moves toward Dr Griffin, who is surrounded by volunteers among Geoffrey’s own workers. Dozens of hands rise to donate blood, and the transfusion succeeds in restoring Geoffrey’s visibility, allowing Griffin to operate and save his life.
