Zac and Cam create a plan to stop the mermaids from getting the trident. They attend a halloween party. Cam goes to mako in the same outfit as Zac. He makes the mermaids follow cam and sirena gets wet by the trap that he and zac set and grows her tail. The mermaids throw Cam (who they think is Zac) against a tree and realise its him. Zac gets the trident, the mermaids reach the trident cave but it closes before they enter. They go back and Zac makes an excuse that he got the desserts. The episode ends with Cam taking the trident back with him to Zacs house.