Derek Rogerson 
The Wrath of the Skull [EPUB ebook] 

Following on from their last adventure, our six girls and Arukot have worked to ensure the wave-making machines have continued to generate unlimited clean electricity. Now, the machines could be converted to help clean the ocean floor of debris deposited by humans.

But then things start to go terribly wrong. Strange mists and rainclouds start to appear at the wavemakers, the girls start to receive flowers and wavemakers and those on them start to dissolve in the clouds.

Is Emilino at the root of the new trouble?