Kathleen Turner plays a writer of adventure stories, Joan Wilder, who has been having trouble selling her works of late because they aren't remotely believable. The basic problem is that the mousy Joan has never had any real adventure in her life.
All this changes when she receives a frantic phone call from her sister, whose is being held prisoner by evil art dealers in Colombia. It seems that sis has mailed Joan a map leading to a valuable treasure. Nasty but cowardly Ralph (Danny DeVito), cousin of the principal villain (Zack Norman), has been assigned to claim the map from Joan.
But upon arriving in Colombia, Joan and Ralph learn that others of a more homicidal bent are also after the map. Joan is rescued by soldier of fortune Jack Colton (Michael Douglas), who isn't quite clear about his stake in the proceedings. Jack and Joan undergo several perilous adventures in the wilds of Colombia.
The treasure turns out to be a valuable jewel, which changes hands (one of them severed!) many times before it is swallowed by an alligator. Joan manages to break free from her pursuers, but Jack is presumed dead. Jack returns at the end of the film in Manhattan to surprise Joan. The sequel to Romancing the Stone was 1985's The Jewel of the Nile.