Western Australia, 1923. Lighthouse keeper Tom Sherbourne and wife Isabel live a quiet, idyllic life on their remote island just a few years after the end of World War I. When a rowing boat washes ashore containing a dead man and a baby, the couple fall for the little girl immediately and decide to raise her as their own, naming her Lucy.

Fast-forward a few years and a chance encounter with a woman named Hannah on the mainland deals the couple a devastating blow.