It's the summer of 1929 and Mhairi MacKinnon is in need of a husband. As the eldest girl among nine children, her father has made it clear he can't support her past the coming winter. On the small, Scottish island of St Kilda, her options are limited. But the MacKinnons' neighbour, Donald, has a business acquaintance on distant Harris also in need of a spouse. A plan is hatched for Donald 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. Mhairi returns as an engaged woman who has lost her heart - but not to her fiancé. In love with the wrong man yet knowing he can never be hers, she awaits the spring with growing dread, for the onset of calm waters will see her sent from home to become a stranger's wife. When word comes that St Kilda is to be evacuated, the lovers are granted a few months' reprieve, enjoying a summer of stolen hours together. Only, those last days on St Kilda will also bring trauma and heartache for Mhairi and her friends, Effie and Flora. And when a dead body is later found on the abandoned isle, all three have reason enough to find themselves under the shadow of suspicion.