After Twenty Years by O. Henry

On a chilly New York night, a man waits to honor a pact to meet an old friend made two decades earlier at the site of a former restaurant; a patrolman briefly checks on him and leaves, and later another man appears and shares memories as they walk, only to arrest him as a wanted criminal and hand him a note revealing that the earlier patrolman was actually the long-lost friend who recognized him but sent a plainclothes detective to make the arrest.

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