Anna Brady, a Boston-based stager, has been in a committed relationship with her boyfriend, Jeremy, for four years, but he has not proposed to her. On Leap Day, Anna's father tells her about an old Irish tradition in which women propose to men on Leap Day, while Jeremy is away at a cardiologists' conference, Anna decides to go to Dublin and propose to him.
Due to bad weather, her flight is diverted to Cardiff, Wales, and she is forced to take a boat to Dingle, Ireland. From there, she hires a local boatman, Declan O'Callaghan, to take her to Dublin, but a series of misadventures force them to make the journey on foot. Along the way, they stop at a wedding, a pub, and Anna's ancestral home, where Declan's grandmother, an ex-nun, tells Anna about the history of their land, and Anna realizes she wants to be with Declan.
In Dublin, Jeremy proposes to Anna before she can execute her plan but tells her he has accepted a position in Dublin. Anna realises that Jeremy is more interested in a bribe from her father to secure a promotion than in her. While trying to retrieve a box she accidentally left on the boat, Anna is caught in an Irish tradition and Declan saves her.
Anna returns to Declan and asks him to help her get to Dublin and, when he refuses, offers him €500 to drive her. Along the way, they discover each other's secrets and, although still wary of each other's presence, it becomes increasingly obvious that there is a spark between them, even if they're both too stubborn to admit it. In Dublin, the weather forces them to spend the night together and they kiss, but Anna decides to go back to Boston, as planned.
Back home, Jeremy apologises and Anna forgives him, but she realises she is not ready to marry him, breaks up with him, and returns to Ireland to find Declan. She discovers that he owns the pub where they stopped during their trip. Anna proposes to him on a Leap Day, and Declan accepts. The film ends with the two passing Dingle's scenic coast, looking happy and in love.
