Watch Siren Season 3 123movies online for free. Siren Season 3 Movies123: The coastal town of Bristol Cove, known for its legend of once being home to mermaids, is turned upside down when a mysterious young woman appears and begins wreaking havoc upon the small fishing town to look for her captured sister who was abducted at the hands of the local military. Marine biologists Ben and Maddie work together to find out who and what drove this primal hunter of the deep sea to land.