Hired Gun

The story's protagonist is a young girl named Robinette Addyson. She is very lonely and always avoids people. It was her last day at school when she witnessed the murder of an international arms dealer. She did not know why the assassin spared her life though she was a witness. The assassin did not kill her but he has plans to kidnap her. What will happen to Robinette? Can she escape from this assassin? What does the assassin plan to do with her?