1926. Tom Sherbourne is a young lighthouse keeper on a remote island off Western Australia. The only inhabitants of Janus Rock, he and his wife Isabel live a quiet life, cocooned from the rest of the world. Then one April morning a boat washes ashore carrying a dead man and a crying infant and the path of the couple's lives hits an unthinkable crossroads. Only years later do they discover the devastating consequences of the decision they made that day as the baby's real story unfolds . . .