Married life had a rhythm all its own, and for Lily and Nathan Harper, that rhythm was as steady and intoxicating as the pull of oars through calm water.

They had been married three years now, the years blending into a beautiful blur of pro seasons, Nathan’s growing role in sports marketing, and the quiet, perfect intimacy that had deepened with every shared sunrise and sunset.

Their Boston brownstone overlooked the Charles, and most mornings began the same way: Nathan slipping ...