The grandson of Dr. Jack Griffin, the original invisible man, has emigrated to the United States and now runs a print shop in Manhattan under the assumed name of Frank Raymond (Jon Hall). In his shop he is confronted by four armed men who reveal that they know his true identity. One of the men, Conrad Stauffer (Cedric Hardwicke), is a lieutenant general of the S.S., while a second, Baron Ikito (Peter Lorre), is Japanese. They are seeking the invisibility formula and threaten amputation if it is not revealed. He just manages to escape with the formula in his hands. Griffin is reluctant to release the formula to the U.S. government officials and only agrees to limited cooperation following the bombing of Pearl Harbor. (The condition is that the formula can only be used on himself). After being rendered invisible, he is parachuted behind German lines on a secret mission. After landing Griffin returns to a visible state and makes contact with a carpenter Arnold Schmidt (Albert Basserman) who reveals his mission. He is to obtain a list of Japanese spies within the U.S. The list was in the possession of Stauffer. Griffin is aided in his task by Maria Sorenson (Ilona Massey), a British spy and the love interest of Stauffer. Griffin manages to obtain the list despite a confrontation with Stauffer, and returns it to his contact. The plot thickens as Griffin steals into a German prison to obtain information about a planned German attack on New York city. —Wikipedia
Surprisingly effective for a Universal Monsters sequel. Aside from Bride of Frankenstein, they tended to be either retreads or (poor) parodies of their originals, but this is another exception. Was nice to see invisibility used in a new way as well as the solid twists and turns of the wartime plot. I will say, though, that it was odd to see Peter Lorre play someone Japanese, especially with his German film roots.