Mary Shannon is a fictional character from the television series In Plain Sight, which aired from 2008 to 2012. She works as a U.S. Marshal in the Witness Protection Program, helping to protect witnesses and their families from dangerous criminals. Mary is known for her strong personality and dedication to her job, often facing personal challenges while balancing her professional responsibilities. In addition to her work, Mary navigates complex relationships with her family and friends. Her character is portrayed by actress Mary McCormack, who brings depth and humor to the role. The series explores themes of loyalty, sacrifice, and the impact of living under constant threat.