Ryn discovers a refuge of injured mermaids that escaped Tia's unhappy takeover. Ben and Xander get caught in a battle with Tia's troops. Maddie feeds Robb half-truths to secure his discretion. Ted explores his family lineage.
The coastal town of Bristol Cove is known for its legend of once being home to mermaids. When the arrival of a mysterious girl proves this folklore all too true, the battle between man and sea takes a very vicious turn as these predatory beings return to reclaim their right to the ocean.