Emily Windsnap, an ordinary girl on land and a magical mermaid in water, is overdue a break from excitement - as her exhausted best friend Shona keeps reminding her! So, promising Shona she'll stay free of trouble and just 'swill out' ('chill out' for mermaids), Emily invites her best friend and her boyfriend Aaron along for a relaxing family holiday in the sun . . . But it seems adventure is hot on her heels - and her tail.