Welcome to Mermaids Rock! The entrance to the mermaid realm in the deep, blue ocean.When the magic whirlpool malfunctions, it sends Marina and her friends to a dark, underground river.Exploring the caves and adventuring along the tunnels, they discover a jungle with amazing wildlife.But then the whirlpool disappears - they're stuck! Stranded, the friends have to use all their skills to return home. The fifth book in an exciting series about the wonders of the ocean, perfect for fans of RAINBOW MAGIC, UNICORN ACADEMY and Holly Webb.