Janus Rock is a tiny and remote island, 100 miles east from Australia’s coast; to the west, vast open water stretches all the way to Africa. Tom, who tends the lighthouse, and Isabelle, his wife, are the island’s only residents.  

One day, a dinghy washes ashore. In the boat are a dead man and an infant, who is still alive. Isabel tends to the baby and is immediately taken with her. The reader can infer from Tom and Isabel’s conversation that they have tried unsuccessfully to have children of their own. Isabel persuades to Tom to wait until morning to report the incident, and against his better judgment, he agrees. 

Seven years before “the miracle” of the baby’s arrival, Tom, a veteran of World War I, successfully interviews for a job with the Commonwealth Lighthouse Service. Tom accepts a temporary post on Janus Rock while the previous keeper, Trimble Docherty, takes medical leave. Trimble has lost his wife; her death and the inhospitable conditions of the island have caused Trimble to become mentally unstable and unfit to maintain his post.

Tom is haunted by the war, and he suffers from nightmares and struggles to put what he saw and did behind him.