Alex Neptune is struggling to get to grips with his new oceanic powers – so the last thing he needs is Haven Bay being attacked by pirates in a ship made of rubbish. The marauders are hunting for the missing egg of the elusive water dragon – and Alex is determined to reach it first to stop them stealing its power. Along with friends Zoey and Anil – plus a clumsy seal, a lock-picking hermit crab and some seriously menacing otters – Alex sets out on a treasure hunt to a secret shipwreck where they must face three monstrous challenges.