A relaxing cruise on a luxury liner turns into a perilous nightmare for Nancy and her gang after one of the men on board, a world-famous mystery writer, receives death threats. When author, John Addmas, and his niece, Cathy, become the victims of several bizarre attempts on their lives, Nancy finds the one vital clue that can save him and races against time to thwart any possible murders from taking place. But solving this mystery means adding her own name to the killer's list of wold-be victims.