Mary Greene was only twelve years old when her mother died of a massive heart attack. She assumed the duties of an adult until she was able to hire a housekeeper. Free to spend more time with her dad she went with him to the rifle range where she discovered she was an outstanding shot. When she was sixteen her father was shot by gangsters shooting at each other in a shopping center. The two criminals walked free which infuriated Mary. Because of the love for her father and the hate towards the gangsters, she became Sheila the Assassin. During her revenge she discovered a secret organization which fought crime. Her expert marksmanship made her a valuable asset to the group. Working with them she eliminated many major criminals. During this period of her life she fell deeply in love.