Carson Drew takes Nancy on a cruise to exoctic Rio de Janeiro. Once on board the Emerald Queen, a beautiful widow named Nina da Silva seems to attract his attention. The problem is, Nina happens to be Nancy's top suspect in a strange caseof stolen gems.
During her investigation someone tries to kill Nancy with a poisonous spider. Then handsome cruise director Rnady Wolfe is wounded by a poisoned dart meant for her. Amid the glittering excitement of Carnival, the teen detective is stalked sy a phantom hit man- who wants Nancy stoped before she can uncover the priceless treacure of the Emerald Queen.