Thora and her family are visiting Flinders Island, which is home for Cosmo the peacock. But where are all his relatives? And what is happening to green sea-unicorn, Shirley. She's sulking and turning yellow.
Meanwhile news from the Mermaid World means that Thora's mother Halla must leave. The Sea Shrew has died and Halla must cast vote in the elections.
Thora is left in the capable hands of her guardian, Mr Walters, who experiences an astounding transformation when he absent-mindedly swallows a Killecrankie crystal when collecting shells of the beach. Suddenly his bad back is cured, he takes up yoga, swears off meat pies and doesn't smoke cigars anymore.
Thora really has her hands full as she's just landed her first job minding bratty young Felicity, who is the daughter of owners of the Deep Breath Hotel where Thora and her family are staying.
When Thora and Felicity stumble upon a factory filled with mysterious dinosaurs with sparkly eyes, Thora's suspicions are aroused and she's determined to get to the bottom of the mystery.