“Ala,” he called. “Ala, my son. It’s Dad.”

Above the number, a strip of paper was taped to the door. On it, in a florid Arabic script, were written the words: Castle of the Assassins. Omar Yussef’s lips twitched in a nervous smile. Nizar always had good penmanship, he thought. That’s a nice joke.

He noticed a button in the center of the door. When he pushed it, a dull bell sounded, but the pressure of his finger also swung the door back on silent hinges. He stepped into the living room of his son’s apartment.

Once more he called his son’s name and added those of his roommates. “Rashid, Nizar? Greetings. It’s Abu Ramiz.”

The room was shabby, furnished with a dilapidated sofa and three dining chairs, one of which was missing its plastic backrest. On the far wall hung a cheap, yellow prayer rug woven with the image of the kaba, the black stone at the heart of the Great Mosque in Mecca. Beside it, a page torn from a magazine had been taped to the wall. It bore a photo of the Dome of the Rock in Jerusalem. On a low table by the door sat a model of the same shrine made of matchsticks, the size of a football, painted gaudy yellow and turquoise. The kind of art our boys make in Israeli jails, Omar Yussef thought.

He crossed the room, with a wariness born of unfamiliarity and anxiety, and smelled the heavy, vinegary homeliness of foule coming from the tiny kitchen. He looked inside, noticed a grimy pot on the stove and a few brown smears of the fava-bean mash at its bottom. He held his hand over the pot and felt some warmth. A magnet advertising a Muslim community newspaper clamped a sheet of paper to the door of the refrigerator. It was a photocopy of the prayer times at a mosque called the Masjid al-Alamut.

Omar Yussef raised his eyebrows. Alamut, he thought. The real castle of the Assassins. These boys didn’t forget my history lessons.