The Light Between the Oceans by M.L. Stedman

This is a wonderful book by a new author--the only bad thing about that is having to wait for another book to be written and to hope that it will be as enjoyable to read as her first book.

Tom is a WWI veteran who survives the war, but at great cost to his mental health--he has been saved on a number of occasions by men who did not survive, and he has witnessed a great deal of man's inhumanity to man, so that when he gets the post as a lighthouse keeper in a remote spot in Australia he is as happy as he has been in a long time.  He gets a bit of respite on occasion, and in his time in town he manages to woo Isabel, a young girl who revives a bit of the person he used to be. 

They live quite happily alone on their island at first, but after several miscarriages, Isabel is a sad woman.  Then a baby comes ashore in a row boat with a dead man.  Isabel convinces Tom to raise the baby as their own, that the man is dead, and the mother is likely to be as well, and  what harm could it do?  Well, quite a lot of harm as it turns out, but one can't help sympathizing with both sides of the story, which had an inevitably sad ending that is paradoxically a joy to read.