Carol Connor, an introverted university biology student, was scratched by a cat which had been used in an experiment. Later that same evening, when she attempted to shut down an experiment in Dr. Baker's lab she was exposed to "Sigma radiation." As a result, Carol found she had developed a cat's agility and claw-like fingernails. She was also superhumanly strong and could see in the dark almost as well as during the day.

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