Old God's Time by Sebastian Barry

Tom Kettle, a retired policeman, and widower, is settling into the quiet of his new home in Dalkey, overlooking the sea. His solitude is interrupted when two former colleagues turn up at his door to ask about a traumatic, decades-old case. A case that Tom never quite came to terms with.

And his peace is further disturbed when his new neighbor, a mysterious young mother, asks for his help.