Mary Richards (Moore) is a single woman who, at age 30, moves to Minneapolis, Minnesota after breaking off a relationship with her boyfriend of two years. She applies for a secretarial job at TV station WJM-TV, only to find it has already been filled. To her surprise, she is offered the position of associate producer for the Six O'Clock News (which pays $10 a week less than the job she originally sought).
At work, she befriends her tough-but-likeable boss Lou Grant (played by Edward Asner), sympathetic, long-suffering newswriter Murray Slaughter (Gavin MacLeod), and buffoonish anchorman Ted Baxter (Ted Knight). Mary's other acquaintances and friends include upstairs neighbor Rhoda Morgenstern (Valerie Harper), a self-deprecating, ex-New Yorker who becomes her best friend, their self-involved landlady Phyllis Lindstrom (Cloris Leachman) and her precocious daughter Bess (Lisa Gerritsen). Characters introduced later are the acerbic, man-hungry host of WJM's cooking program, The Happy Homemaker, Sue Ann Nivens (Betty White), and sweet-natured, soft-spoken Georgette Franklin (Georgia Engel), Ted Baxter's girlfriend and then wife.