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.

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...

Of all the creatures in the ocean, sea horses are Echo Reef's favorite. They're sweet and gentle and they glide through the water so gracefully. When Echo discovers that Rocky Ridge, one of her Trident Academy classmates, has his own pet sea horse, she wants one right away. Not everyone agrees sea horses should be pets, however. Perhaps they are happiest when swimming freely. But Echo thinks that if Rocky can make a sea horse happy, she can too! Can't...

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.

When Echo, who is tired of sharing everything with her sister Crystal, finds an artifact from the human world, she and Crystal fight over ownership and are forced by their mother to get along.

Longing for onstage stardom, Pearl auditions for the third-grade play and gets the part of the evil sea witch while her best friend is cast in the lead, a situation that challenges their friendship.

When Echo twists her tail while riding Rocky's seahorse, she is told she cannot perform as the star tail flipper on Trident Academy's team, and she must come up with a way to help her team win.

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.

Echo's third grade class visit the Titanic and figure out a way of including their new classmate, Anita, who is confined to a wheeled chair.