The series, which takes place in Frankfurt am Main, Germany, is notable as being the first, and as of yet, one of the few commercially successful German detective series to have a female lead character (others include Bella Block and Rosa Roth).
The main character is Inspector Lea Sommer, played by Hannelore Elsner. Sommer is divorced with custody of her teenage son, Daniel. She is looking forward to a new relationship with her new boyfriend, Jonathan. Although Lea and Jonathan telephone each other frequently, he has never actually been seen or heard on screen (see unseen character).
Sommer was originally paired with Nick Siegel (Til Schweiger), but in a 1996 episode, Siegel was shot to death by an escaping criminal. His last words were "Lea, ich fühle mich so kalt" ("Lea, I feel so cold"). Sommer's current partner officer is Jan Orlop.