Mara found the key in the pocket of her grandmother's winter coat, a small brass thing worn smooth by decades of handling, the kind of object that seems to have been carried for a reason. Her grandmother had died in the spring, and in the weeks of sorting and packing nothing in the house had turned out to fit it: not the cupboards, not the old sewing box, not the shed at the bottom of the garden. All the same, Mara could not bring herself to throw it away.
That evening she took the last ferry across the bay. She was turning the key over in her fingers, watching the harbor lights slide past, when she noticed that the old man sitting opposite was doing exactly the same. His key was identical to hers. "Where did you get that?" he asked, so quietly that she nearly lost the words under the engine. "From my grandmother's coat," said Mara. The old man lowered his eyes and smiled, as though a very long wait had just been ended by a stranger. "Then you must be her granddaughter. My name is Aldo. Your grandmother and I were best friends when we were children. Sixty years ago we locked a wooden box under the old pier, and we promised to open it when we were both old."
The next morning, at low tide, they walked out together over the wet sand and found the box, swollen and salt-stained but still shut. Inside lay two small paper boats and a note in a child's handwriting: "We'll sail again." Aldo laughed and cried at the same time, and Mara found that she could not tell the two apart. She tore a page from her notebook, folded a new boat, and together they set it on the water, an old man and a young woman keeping a promise that had been made for them long ago.