To ride across the bay at this hour is to see Shep’s Island at its most beautiful. The light of the setting sun sends sparks off the water in every direction. On this particular night, there is electricity in the air. The water runs deep here along the coast of Maine. It is bitter cold and black beneath the glimmer on the surface. The wind bites into the skin. Seabirds lift and soar, chaotic and fluttering, then change direction. They look back, beak over wing, as if to say goodbye. The ferry churns along, and Shep’s comes into view. The smallest one in a chain, this island is the third stop on the ferry. Its contours blur against the horizon. But get a little closer and a line of trees comes into focus, leaning forward, beckoning, bent by the Atlantic winds.

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There used to be a long luxurious beach on the east side of the island, a stretch of soft sand protected by massive boulders at each end. But the seas rise a little more each year, the island gets smaller still.…