Sequel to Mermaid H2o just add water

What happens when Melody's ex boyfriend, and ex bestfriend, come to town? Will Cleo,Rikki,Emma,Melody,Lewis,Billy and Riley, be able to keep their true identity secret? What happens when Emma finds six mysterious necklaces, identical to Melody's and gives them out to all the Mermaids and Mermen. All rights go to whoever made H2o just add water