Polvina is doing the boys' homework again and Ester and Tubarina have had enough. They're going to help Polvina be bad instead of good for a change.
Marcello and Hugo are having a campout outside the Shark Palace. As the girls watch them, Ester and Tubarina decide to have Polvina play a trick on them, saying that she has to be bad to do something good. They drape a blanket over Polvina and have her make scary noises. After they realise that it is probably not going to work, Polvina attempts to get the blanket off, but she trips and disturbs some parrotfish, who begin poking at her before she tries to get away.
Seeing that the girls are attempting to give them a scare, the boys decide to give them a scare first, but they get scared and find themselves chased by the parrotfish and Polvina, who still has the blanket over her, causing a mess in the garden.
The next morning, the Shark King sees this and has Marcello and Hugo clean the mess up, not believing their story about a sea monster and the parrotfish. Polvina feels bad about it and decides to tell the Shark King, but Ester and Tubarina prevent her from doing so as they want to teach the boys a lesson.
After struggling to work out the right thing to do, Polvina decides to talk to Marcello and Hugo, but they tell her first that they have been feeling bad about getting her to do their homework. Following this, she manages to evade Ester and Tubarina as she tells the Shark King the truth about everything that happened. When asked by Polvina, the Shark King tells her that he doesn’t think she is a bad princess, unlike Ester or Tubarina.
As they clean up the garden instead of the boys, Polvina tells Ester and Tubarina about what happened. While Ester and Tubarina insist that Polvina can never be a bad princess, Polvina says that she can be if she wants to. After failing to show them how bad she can be, Polvina does something “bad” when she accidentally disturbs the parrotfish again, leading them to poke Ester and Tubarina.