One day a simple fisherman (Colin Farrell), trawling off the Irish coast where he makes his living, catches a beautiful and mysterious woman in his nets. She appears to be dead but, miraculously, comes back to life before his eyes.
The fisherman, Syracuse, is a devilish, irresponsible loner, separated from his former wife and distanced from Annie, his wheelchair-bound daughter. But everyone's drab and ordinary life is about to change with the arrival of the ethereal Ondine, the woman from the sea, who may or may not be real. Annie has a powerful belief in folklore, and the world-weary Syracuse soon finds himself believing that the stranger may well be a myth come true, a woman sent to change his life and a powerful force for love and hope.
As Syracuse falls under Ondine's captivating spell, he discovers that his relationship with his daughter undergoes the same kind of magical transformation.