It focused on Scarlet O'Neil, a plainclothes superhero (and one of the first superheroines) who had the power of invisibility. Scarlet used this power mostly to help out strangers in need and help the police catch dangerous criminals, as explained by comics historian Don Markstein: She also appeared in comic books, Big Little Books and a 1943 prose novel. In 1950, the title was reduced to simply Scarlet O'Neil and changed again in 1955 to Stainless Steel.