It's the summer of 1929 and Mhairi MacKinnon is in desperate need of a husband. As the eldest girl of nine children, her father has made it clear he can't support her past the coming winter. On her lonely island home of St Kilda, Scotland, her options are limited, but one of the MacKinnons' neighbours has a business acquaintance on the Isle of Harris looking to marry. A plan is hatched for him to chaperone Mhairi and make the introduction on his final crossing of the year, before the autumn seas close them off to the outside world once more. Mhairi returns as an engaged woman who has lost her heart -- but not to her fiancé. In love with the wrong man but knowing he can never be hers, she awaits the spring with growing dread, for the onset of calm waters will see her sent across the water to become a stranger's wife. When word comes that St Kilda is to be evacuated in August, the lovers are granted a few months' reprieve, enjoying stolen hours together. But come the end of the summer, Mhairi will be separated from her love, her family and friends, and everything will change forever.