|Season 1, Episode 7|
|Air date||June 19, 2007|
The Biggest Fish
Polvina's diary has been stolen, and everyone at school is searching for it. Ester and Tubarina want to help Polvina, but deep down are more intent on reading it to find out exactly what Polvina's secrets are!
Miss Marla introduces the students to the Salacian Library so they can work on their projects. While struggling to pick a topic for her project, Polvina writes in her diary, but is interrupted by a creature swimming in the shadows. Believing it to be Marcello, Polvina goes to see where he is, but he is nowhere to be found and when she returns to her table, her diary is gone.
Polvina finds Marcello and Hugo and confronts them over stealing her diary, but she is mistaken when she finds that they are reading a joke book with a red cover, the same colour as the cover of her diary. Piqued, Marcello and Hugo decide to follow her.
Polvina searches for her diary around Ester and Tubarina’s table. When they learn that Polvina does have a diary, Ester and Tubarina probe her with questions about what is in it. Marcello and Hugo, who are listening nearby, decide to find Polvina’s diary so they can read her secrets. Right at that moment, Isa’s red schoolbag is stolen by what she claims is a lionfish. Soon after, Lia’s red pencils are stolen by what she claims is a solefish.
The creature, apparently a sea snake, swims past the girls and they follow it, with Marcello and Hugo hot on their trail. They are led to a basement of the library, where the girls are confused at the true nature of the thief. Hugo lets slip his and Marcello’s motives of finding Polvina’s diary. The boys and girls, save Polvina, go their separate ways to chase the creature. They end up tackling each other, but despite this, they manage to find the stolen items. Polvina goes another way and manages to find the creature herself, spotting its ability to switch forms in the process.
Marcello grabs Polvina’s diary. Ester grabs it off him, but neither she nor Tubarina can bear to read it. Marcello takes it back, only to give it back to Polvina when she arrives with the creature before leaving with Hugo. Polvina explains that the creature is a mimic octopus, which can disguise itself as a lionfish, a solefish or a sea snake. She also reveals to Ester and Tubarina that there is nothing much in the diary apart from ideas for school projects. The mimic octopus promises not to steal things again, because he liked collecting red things to put around his den. Out of suggestion, Polvina decides to do her project on the mimic octopus. She puts her diary in her bag, out of sight.
- The synopsis implies that everyone is looking for Polvina's diary when it is really only five people looking for it, namely Marcello, Hugo, Ester, Tubarina and Polvina herself.