Cam apologizes to Zac for his betrayal but keeps the trident hidden. The girls look forward to returning to the pod. Everyone catches on to Cam's scheme and races to Mako Island. Will they stop Cam and be allowed to return to the pod?
Erik is determined to activate the Merman Chamber even though Ondina begs him not to. Zac feels powerless without his magic and seems to give up. The mermaids decide to try to destroy the chamber. The chamber's true purpose is revealed.
While listening to Sirena sing, Lyla has an idea. If Sirena sings The Enchantment Song to Zac, he will fall under her spell. Everything goes south when David hears the song and falls in love with Nixie.
On the night of the full moon, Sirena takes Evie to the Moon Pool to help her control the moon spell. Veridia, Ondina, and Mimmi go to the Merman Chamber where Zac and Erik are trying to unlock it. Secrets are revealed.
Lyla goes to check that the trident is still hidden and watches Zac and Cam find it. While attempting to wrestle it away from Zac, it zaps her into unconsciousness. Now realizing the extent of the trident's danger, Zac must make a choice.