Zac and the mermaids are determined to stop Erik from controlling Mako. As the full moon nears its zenith, the merman chamber draws the water from the moon pool and the chamber’s true purpose is revealed – to drain the magic from all mermaids. Zac risks his life to shut the chamber down and restore the mermaids' magic. The pod is able to return to Mako. Evie gets a moon ring and Ondina, Mimmi and Sirena are welcomed back to the pod.