Syracuse, an Irish fisherman (Colin Farrell) is out fishing one day and catches a mysterious woman in his net (Alicja Bachleda). She gives her name as Ondine, which means “she came from the sea”. Slowly but surely Syracuse falls in love with his mystery woman, but his daughter Annie (Alison Barry) develops a belief that Ondine is in fact a selkie. In Celtic myths selkies are seal/woman creatures that are able to take off their seal coats and become human. They traditonally live on land for seven years and then seven years in the sea, and Annie hopes that Ondine will now spend seven years on land with them and use her magical powers to cure Annie's kidney failure. But there are many mysteries surrounding Ondine, not least the man that lurks around town spying on her, who could well be her selkie husband come to take her back to the sea.