Murder, She Wrote (1984)

Angela Lansbury's Jessica Fletcher is the patron saint of the genre: a widowed mystery novelist from the Maine town of Cabot Cove who keeps tripping over bodies and quietly outthinking the police. The formula never varies much, which is exactly its appeal, with sunny locations, a parade of guest stars and a final scene where Jessica spots the one detail that does not fit. With twelve seasons to choose from, it is the ideal show to put on when you want a puzzle without any risk of a bleak turn.