Hart aber Herzlich: Alte Freunde sterben nie (1994)

The Harts find themselves in the middle of a dangerous murder plot, but it isn't clear if the plot it a famous author's fictional murder-mystery, or an actual murder plot, until Jonathan finds himself the unsuspecting target of a killer. It begins to look like the culprit behind the plot is an old friend, Frank Crane, but there may be a connection to a corporate takeover of Hart Industries as well.