When Nancy and her friends vacation in a California beach house, they discover someone is dumping trash on the beach, and Nancy suspects both reality show sisters the Casabians and a suspicious owner of a spa.

When the polluted beach at their Malibu condo forces them to relocate to a holistic spa next door, Nancy Drew and her friends investigate the spa's motivational guru, whom they believe may be responsible for the local ocean garbage dumping.

The wicked Mantora sets another trap for the young mermaids by littering a beach where a seal family lives, and Scarlett's bossiness interferes with the clean-up effort, further delaying the mission to bring the magic crystals home.

"When Kenzie slips on her mermaid tail, she becomes Mermaid Kenzie, protector of the deeps. One day as Kenzie snorkels around a shipwreck, she discovers more plastic bags than fish. Grabbing her spear and mermaid net, she begins to clean up the water and the shore--inspiring other kids to help"--

Hubie transforms into Earthman, defender of the environment, to battle Trashman's army of litterbugs.