Joan Wilder (Kathleen Turner) is a New-York based writer of cheap romance novels. She's a bit clumsy. One day, she finds her condo, where she lives with a cat, in a mess. Right away she has a frightening call: her sister Elaine (Mary Ellen Trainor) has been kidnapped in South America. She decides to go there to save her. There is a map which leads to a huge treasure.
She has to take a bus to Cartagena, in Colombia, but she has trouble with the language spoken there, Spanish. She gets on a coach, but she is afraid she has taken the wrong one, so she asks the driver (Camilo García) while on route. The driver gets distracted because he can't understand her and has an accident. The bus is a wrekage.
Joan asks adventurer Jack T. Colton (Michael Douglas), to take her there. He accepts becasue he wants the money to buy a ship. They are followed by some mysterious Latin men and soldiers, commanded by corrupt policeman Zolo (Manuel Ojeda). Ralph, (Danny DeVito) is organizing their capture from far away, because he wants the map as well. He is even less equiped to life in a poor Latin American country than Joan is.
Joan and Jack fall down a spring, they have to cross a wide river, and eventually they get lost. They find a crash airplane with boxes of marihuana, and they spend the night there, because it's pouring down with rain. When they leave the next morning, after Jack has saved Joan from being beaten by a poisonous snake, they arrive to a small village.
They ask for a phone or a car there, but several dangerous-looking men tell them there is not any. Asking at a mansion, they are helped because Juan (renown film director Alfonso Arau) recognises Joan. Juan calls her Juanita Wilder, and says that he always reads her novels to the dangerous men. That way they ran away.
Ralph finds them, dressed in Colombina-like outfits. Zolo also pursuits them. They fight each other, they ran after one another, and there is the suspicious that Jack is going to betray Joan at any moment because of the treasure. They are about to be eaten by crocodriles all the time, which is a funny moment. All the main characters are about to fall in the crocodile pond while fighting and going back and forth in pursuit of the treasured green diamond.
Finally, Joan and Elaine are together again. Soldier of furtune Jack and Joan must face their mutual attraction, although they are completely opposites in many aspects.
A true modern classic!