Ben and Xander are left dealing with a shocking discovery about Chris and his connection to the military. Meanwhile, Helen and Maddie reluctantly seek help from the hybrids as the threat of extinction looms over the mermaids. Ryn encounters the journalist who continues to chase his theories on mermaids to increasingly desperate ends.
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.