Welcome to Mermaids Rock! The entrance to the mermaid realm in the deep, blue ocean. When animals start disappearing from the reef into the mysterious Midnight Realm, Naya and her friends investigate! There they find a glowing cave with a tentacled monster lurking within. Then it traps Luna and the friends launch into action. Naya will have to get inventive if she's going to pull off her rescue mission... The fourth book in an exciting new series about the wonders of the ocean, perfect for fans of RAINBOW MAGIC, AMELIA FANG and Holly Webb.