玛丽（玛丽·麦克科马克 Mary McCormack 饰）有这一个秘密的身份，那就是联邦保护证人组成员，她的工作，是保证那些鼓起勇气成为证人的目击者和受害者们的安全，帮助他们躲避罪犯的追杀，将他们送往陌生的城镇开始新的生活。马肖（Fred Weller 饰）是玛丽的搭档，虽然性格大相径庭的两人总是会产生种种摩擦，但是他们不得不承认，在工作中，对方都是自己最信赖的好帮手。 　　玛丽有一个复杂而又麻烦的家庭，母亲金克斯（莱斯莉·安·华伦 Lesley Ann Warren 饰）整日不务正业，沉溺于酒精带来的麻痹之中。妹妹布兰迪（妮可·希尔兹 Nichole Hiltz 饰）则被男友恰克（蒂姆·科勒赫 Tim Kelleher 饰）关了迷魂汤，竟然想帮他运送一批冰毒出境。Mary Shannon is a U.S. Marshal in the witness protection program who spends her time relocating federal witnesses.. Based in Albuquerque, New Mexico, Mary works with her partner, Marshall Mann, to place criminals and innocent witnesses into new lives. When not putting her life on the line to protect federal witnesses, Mary attempts to manage her dysfunctional family, including overly dependent mother, Jinx, and younger sister, Brandi, both of whom live with her. Between work and family, Mary has little time for boyfriend Raphael Ramirez who plays minor league baseball.