In a distant watery corner of the Explorers Realm, a submarine engineer, Ursula, is determined to become an explorer. Unfortunately, she hides an extraordinary secret, which makes her the sworn enemy of the Ocean Squid Explorers' Club were they ever to find out. But when The Collector threatens the Club, Ursula throws caution to the wind and leads an expedition through treacherous waters, filled with gremlins, aboard the Blowfish submarine - and joined by her friends Max, Genie and Jai - and even her idol Stella!