Dilo the dolphin has a star on his dorsal fin. It signifies that he has a mission. Despite numerous attempts Dilo is unable to find out what his mission is until he sets off on a new adventure in the company of a suckerfish seeking a free ride. On this latest quest Dilo unveils the Secret of Atlantis, and surprisingly, the reason for the star on his dorsal fin.

At the same time Dilo is making these discoveries Mission Pelican is on its way to solve another mystery. Why should a pelican appear in Lighthouse Bay thousands of miles away from its usual habitat? Mervin Swaddleback reluctantly joins the crew onboard the research vessel Merlin to find out.

Mervin Swabbleback is under orders from his employers – a credit finance company - to provide stories to convince investors of its concern for the environment. Mervin Swaddleeback, however, knows there is a more sinister reason for his presence onboard Merlin.