The Octonauts and the Poisonous Mermaid Spell is the 24th episode of Season 4.
Kwazii is cursed by a Poisonous Mermaid while collecting pearls and rubies in her lair he thought was an ordinary cave for his sister and falls into a deep sleep. So Peso and Barnacles go into the Midnight Zone to find the rarest kelp, the Black Kelp, to cure Kwazii before he sleeps forever.
The episode begins in
(Narrating): The Octonauts and the Poisonous Mermaid Spell.