It's a couple of years since the events of the first game and Jessica - the former advertising executive turned treasure hunter whose exploits formed the story of the first Deep Blue Sea - has disappeared. Her younger sister Melissa receives a worn postcard with a note in Jessica's handwriting written in the secret code that the two sisters invented when they were young. The note tells Melissa to go to Billinger Island, which is where the search for her sister - and her own adventure - begins.