ZacisateenageboywhodecidestocamponMakoIsland,unawarethatthreemermaids,Sirena,NixieandLyla,whoareguardiansoftheisland,arewatchinghimThatnight,whenthefullmoonrises,theboycomesintocontactwiththemagicwateroftheMoonPoolThefollowingmorning,ZacwakesupdiscoveringhehasbecomeamermanwithafishliketailandtheabilitytocontrolandmanipulatewaterHisnewfoundmermanabilitieswillcauseproblemsforthemermaids　　Thethreemermaids,curiousaboutlivingonland,aretransformedintohumanswhileinthemoonpoolduringafullmoon,nowhavingtheabilitytolivelikehumans