Mermaid Echo is doing tail flips because she's going to see her favorite under-the-sea band, the Rays. They're performing for Pearl's birthday party and everyone at Trident Academy is invited except Echo's best friend Shelly.

Unable to comprehend a beloved librarian's imminent marriage to a cafeteria worker who seems to be perpetually grouchy, Pearl becomes jealous when Echo, Shelly, and Kiki are all asked to be flower girls.

A shark has been spotted in Trident City! Pearl Swamp is so scared, she needs a shark Guard to escort her to and from school. She doesn't trust anyone who likes these terrifying creatures, especially Kiki Coral, who isn't nearly as frightened as Pearl. And to make matters worse, Pearl accuses Kiki of stealing her precious pearl necklace! Will the sharks destroy the peace of their sparking city? Or will the mergirls have to swim in dangerous deep-sea...

Shelly Siren loves playing on Trident Academy's Shell Wars team. But is she ready to complete in the Shell Wars Championships in the fintastically famous city of Atlantis? As part of their trip, the mergirls get a tour of Atlantis and swim through Poseidon's Temple where Shelly sees a spookfish, which according to legend, carries a horrible curse.

Wanting to help a lost baby polar bear return home, Kiki Coral and her mermaid friends worry that the cost of the bear's transportation will prevent them from seeing a concert performance of their favorite boy band.

While preparing for a unit on storytelling, the mermaids of Trident Academy learn of a legendary pirate treasure in their own city and Pearl decides to find it, despite a warning that it is guarded by a ghost.