The wife pleads with her husband to keep the baby and pretend it's their own. He feels uncomfortable but ends up agreeing.
Existence here is on a scale of giants. Time is in the millions of years; rocks which from a distance look like dice cast against the shore are boulders hundreds of feed wide, licked round by millennia, tumbled onto their sides so that layers become vertical stripes.... it astounds him that the tiny life of the girl means more to him than all the millennia before it... (p. 150)
The Light Between Oceans by M.L. Stedman lays out the moral dilemma. As the child turns four, just whose child is she? Is it 'right' to return her to her birth mother, now a stranger?
The premise is fascinating, as is the description of life as a lighthouse keeper in the early 1900s. Set in Australia, the seasons often caught me unaware. Like when the child wanders off in December without a coat, and people are thankful because the nights are still warm.
The ending was incredibly sappy though. It seemed to aim for tearjerker, but totally disappointed me, as it skipped over decades in an attempt to neatly tie up loose ends. The saccharine family reunion really didn't work for me, and I can't help but wonder if the author or publisher held the pen at that point.