The book arrived on a Tuesday, secondhand, smelling faintly of someone else's house. Marguerite had ordered it for the title alone — An Atlas of Impossible Crossings — and she read the first chapter standing up in the hallway, coat still on, the way you drink water after a long walk.

On page 141 she found a bookmark. Not a nice one. A bus transfer, folded twice, gone soft at the creases. On the back, in pencil, in the smallest handwriting she had ever seen:

if you've come this far, keep going.

She looked, of course. Everyone looks. The transfer was from a city she had never visited, dated nine years back, punched at 11:52 at night. Someone had been on a bus near midnight, reading about impossible crossings, and had made it to page 141 before the driver called their stop.

Or before they gave up. That was the other reading, and it bothered her more than it should have. You don't leave a note like that for yourself. Keep going is what you write when you know you won't be coming back, and you can't stand the thought of the crossing going unmade.

She read on. Page 141, it turned out, was where the book stopped being about maps.

It took her the rest of the winter. Some chapters she read twice; one she read aloud, alone, because it seemed to want it. When she finished she sat for a while with the cover closed under her hand, the way you keep your seat for a moment when the bus has already stopped.

Then she took an old ferry ticket out of the drawer, wrote four words on it in pencil, tucked it at page 141, and gave the book back to the shop on the corner — for the shelf, she said, not for credit.

You already know what she wrote.