Something Fishy This Way Comes
Professor Rotwood talked about the sea and explained about magical creatures under it. He then saw Jake, Spud and Trixie playing with a Toy Stick that Spud made, Professor Rotwood then got mad and sent him to the principal's office.
In the principals office, she talked to him about his record and his behavior in the past year, Jake then saw Fu Dog in the window telling him to go downstairs. Jake left immediately and the principal started to wonder about Jake and wanted to spy on him.
Outside, they go to an underwater place where mermaids are. There, Jake sees Silver who explained to him about a magical creature called the Kelpie 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 kelpie.
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 heard screams, gnomes were running away from the monster, he tried to find the Kelpie, but he is hiding.
When he got back, Jake heard 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 screamed.
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 kelpie. 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 Kelpie. 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 went to Principal Derceto's house to "trap" her, he told her about the handcuffs they started fighting, but Jake pushed her to the water and trapped 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 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 kelpie, Grandpa sees this and fights him, but the monster knocks him out, he absorbed the powers and transformed into him when Jake appears and fights him. The kelpie then turns to a unicorn, then a gnome and then a troll fighting Jake.
Jake grabbed a piece of pole and put it in the kelpie's mouth, Principal Derceto then Head butted the Kelpie and knocks him out.
In the beach, the merman police take the kelpie away, Fu Dog yelled out to the kelpie 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 wanted to go with her but when they go underwater, he can't breathe so he went 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 screamed in joy, then he told them that he is now the new principal. Everyone then got disappointed, and Jake sighs sadly and says "Aww Man!".
- In European mythology, a kelpie was a sea monster that took the form of a white horse to lure sailors to mount them which they then dragged underwater and devoured. The kelpie depicted here rather can turn into any magical creature whose power it has consumed.
- Spud reveals his fascination with merfolk and even attempts to "become" a merman.
- Oddly the mermaid city, while underwater, is mostly filled with air (possibly to acommodate land visitors). The mermaids themselves seem to have no problem traversing land anyway, as seen when two mermen escort the captured kelpie and are seen slithering across the dock on their tails.