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Ever since he had lived alone, Andrés switched off his lamp at a little before midnight. In the building across the street, a third-floor window went dark at the exact same instant. It wasn't a signal, he told himself: it was a friendly coincidence, two insomnias keeping the same hours. He grew fond of it, the way you grow fond of a traffic light that is always green for you.
One Tuesday he decided to test it. He left the lamp on at twelve. At one. At three. The window across the street stayed lit, exact, without a flicker, as if it too were waiting.
In the morning he went down to ask. The caretaker of the building across the street shrugged: the third floor had been empty for years, since what happened to señora Elvira. Not even furniture left, she said. Not even light bulbs.
That night Andrés switched off his lamp at a little before midnight. Across the street, the light took one second longer than usual to go out. One exact second. Just long enough to make it clear who was keeping whom company.