Mr. Mallet, the Guardian of the Aquarian world, sets out on a new adventure to find the secret door in the Aquarian world that his mother mentioned. He consults with Lila, his closest friend, and together they embark on a journey to explore the vast underwater world.

They encounter many challenges, including dangerous sea creatures and treacherous currents. But Mr. Mallet's determination and Lila's quick thinking help them overcome each obstacle. As they journey deeper into the Aquarian world, they begin to uncover clues that lead them to the secret door.