Frank Griffin Jr. (Jon Hall), grandson of the original invisible man, is owner of a print shop in New York City, calling himself Frank Raymond. He is confronted in his shop by four armed men who say they are foreign agents, and they know who he is. Conrad Stauffer (Sir Cedric Hardwicke) is a lieutenant general of the S.S.. Another, Baron Ikito (Peter Lorre) is spying for the Japanese Empire. They threaten to amputate his fingers, one by one, until he gives them the formula for invisibility.
Griffin manages to escape. He is reluctant to release the dangerous formula to the U.S. government, but after Pearl Harbor, he makes a deal. The formula can only be used on himself. Parachuting in behind German lines, he injects himself, strips off his clothing, and becomes invisible. He evades the German troops and makes contact with a coffin-maker named Arnold Schmidt (Albert Basserman), who reveals his next step. Griffin must obtain a list of German and Japanese spies in the U.S. from General Stauffer, who is in possession of the document. Aiding him will be Maria Sorenson (Ilona Massey), a double agent and love interest of both Stauffer and his second-in-command, Karl Heiser (J. Edward Bromberg) of the Gestapo.
She will attempt to get information from Heiser during a romantic private dinner, with Griffin as an unseen witness. A bit drunk from champagne, Griffin can’t resist using his invisibility to play tricks on Heiser. Angered, Heiser places Sorenson under house arrest. By way of apology, Griffin reveals himself to her by putting on a robe and smearing facial cream on his face. They find themselves attracted to each other. Conrad Stauffer returns from the U.S. and meets with Heiser, Sorenson, and Ikito. Learning of Heiser’s romantic dinner with Sorenson, the jealous Stauffer has Heiser arrested and arranges a trap for Griffin. He walks into the trap but still manages to get his hands on the list and covers his escape by setting a fire. Then he takes the list to Arnold Schmidt to have it transmitted to England.
Ikito pries into the matter and Stauffer has to hide his loss of the list. Both of them start to hunt for Griffin. Meanwhile, Griffin has penetrated a German prison to obtain information about a plan to attack New York City. He helps Heiser escape his execution in exchange. Schmidt is arrested and tortured by Stauffer. Griffin believes that Sorenson has betrayed the cause and confronts her, only to be captured by Ikito’s men. Griffin and Sorenson are taken to the Japanese embassy, but escape. Ikito kills Stauffer and commits ritual suicide.
Heiser takes command but can’t stop Griffin and Sorenson from escaping. They take over one of the bombers slated for the New York attack and destroy the other planes. Heiser is shot. The plane is shot down and Griffin passes out from the effects of the serum, but Sorenson parachutes with him to safety. Later, Griffin is in the hospital with cream on his face. Left alone, he and Sorenson kiss.
The film was directed by Edwin L. Marin from a screenplay by Curt Siodmak. It’s a war-story and not a spook show. George Waggner was associate producer. John P. Fulton and Bernard B. Brown were nominated for an Oscar for special effects. It was quite successful as a propaganda film, with some car chases and abundant use of the invisibility trope, both seriously and comically. Peter Lorre and Cedric Hardwicke transcended their roles and pretty much stole the movie. The rest of it did not impress critics that much and Ilona Massey, when asked, could not remember anything about it.