Seahorse SOS (The Secret Mermaid #7)

Molly is called back by the Mermaid Queen because the mermaids desperately need her help. All the whales, turtles, seahorses, octopuses and dolphins have vanished from the seas and the mermaids expect dark magic is at work. Molly believes the answer to their whereabouts might lie in a strange sparkly ball she spotted in a rock pool.