The episode starts off with Professor Rotwood talking about the sea and explaining about magical creatures under it. He then sees Jake, Spud and Trixie playing with a Toy Stick that Spud made. Rotwood then gets mad and sends Jake to the Principal Derceto's office.
In the principal's office, Derceto talks to Jake about his record and his behavior in the past year, Jake then sees Fu Dog in the window telling him to go downstairs. Jake leaves immediately and the principal starts to wonder about Jake and wants to spy on him.
Outside, they go to an underwater place where mermaids are. There, Jake sees Silver who explains to him about a magical creature who escaped a year ago. Jake thinks they called him to tell him to capture him but they called him to warn him about the monster.
In the shop they discuss about how Grandpa doesn't give Jake a break, his parents are out of town and they should be having a party, Fu Dog tells them about a dating service and Jake gets the idea of finding Grandpa a date, but the next day when all these women magical creatures come, none of them seem to interest him and Grandpa finds out that it was Jake so he gets in trouble.
In the bathroom, Jake hears screams, gnomes were running away from the monster, he tries to find the monster but he is hiding.
When he gets back, Jake hears Grandpa and a woman laughing. When he goes downstairs he sees Principal Derceto and Grandpa talking. Principal Derceto tells Jake that at first she didn't believe him about his parents being out of town, Grandpa suggests they should talk about Jake's problem, they hold hands and she says "It's a date". Jake then screams.
Later, Trixie and Jake talk about what happened. Then, Jake goes to look for the creature after hearing screams of the attack. Right there he finds Principal Derceto as well, he sees a piece seaweed in the wheelchair of Principal Derceto, she tells him that they went to the beach, she then leaves.
In the school, Jake and Trixie as well as Spud are trying to get in Principal Derceto's office, Jake thinks that she is the monster. When they go inside Jake finds the rusty handcuffs that the monster used when he was underwater trapped. Spud passes his finger and tastes of them, and tells Jake and Trixie the place and time of the handcuffs. This gives Jake more proof that Principal Derceto is the monster. They hear her come in and Jake, Trixie and Spud jump out of the window. Principal Derceto comes in and sees the trash has been knocked down, then you see the shadow and see Principal Derceto standing up.
In the shop, Jakes tells Grandpa that Principal Derceto is the "monster" that escaped, but Grandpa doesn't believe him, thinking that is a way to break them up.
Jake goes to Principal Derceto's house to "trap" her, first telling her about the handcuffs. They start fighting but Jake pushes her to the water and traps her. She then tells him that he is the monster, but Jake tells her that he thought that about her. Principal Derceto tells him that she is an undercover mermaid sent to try and trap the monster. Jake then gets worried about Grandpa that he is alone.
In the shop, Fu Dog's date is with him and Grandpa, Fu Dog leaves to get her a drink, the dog then turns to the monster, Grandpa sees this and fights him but the monster knocks him out, he absorbs the powers and transforms into him when Jake appears and fights him. The monster then turns to a unicorn, then a gnome and then a troll fighting Jake.
Jake grabs a piece of pole and puts it in the monster's mouth, Principal Derceto then head butts the monster and knocks him out.
In the beach, the merman police take the monster away, Fu Dog yells out the monster about pretending to be his date. Jake then tells Principal Derceto and Grandpa that it is okay with him if they go "steady". Principal Derceto tells him that she was sent to another undercover mission. She has to leave. Spud wants to go with her but when they go underwater, he can't breathe, so he goes back.
At school, Jake and Trixie and Spud talk about Principal Derceto leaving. Jake tells them that it is now better because he gets a clean start with the new principal, whoever it is. Professor Rotwood tells the class that he won't be their teacher anymore, everyone screams in joy, then he tells them that he is now the new principal. Everyone then gets disappointed, and Jake sighs sadly and says "Aww Man!". The episode ends on that.
- Jake Long
- Luong Lao Shi
- Fu Dog
- Arthur Spudinski
- Trixie Carter
- Dolores Derceto
- Shark People
- Jonathan Long (mentioned)
- Susan Long (mentioned)