The mermaid's dolphin / Coral Ripley.

Includes excerpt from: The sea unicorn.

When three friends rescue a dolphin caught in a fishing net, a young mermaid named Marina is so grateful to them for rescuing her naughty pet dolphin, Kai, that she gives them magical shell bracelets and leads them to her home, the amazing underwater city of Atlantis. The merfolk who live there are responsible for protecting the seas and all the creatures who live there. Unfortunately, Atlantis is in a bad way because pollution is destroying it and there aren't enough mermaids to help all the sea creatures in need. The mermaids' enemy, Effluvia, wants to destroy Atlantis and all the mermaids. She has stolen the precious Treasure of Atlantis, the magical pearls that protect Atlantis, and scattered them all across the seven seas. the girls promise to help the mermaids get the pearls back.