THE INVISIBLE MAN RETURNS (1940)
The owner of a coal mining operation, falsely imprisoned for fratricide takes a drug to make him invisible, despite its side effect: gradual madness.

THE INVISIBLE WOMAN (1940)
An attractive model with an ulterior motive volunteers as a guinea pig for an invisibility machine.

INVISIBLE AGENT (1944)
The Invisible Man’s grandson uses his secret formula to spy on Nazi Germany.