One boy, seated toward the rear of the boat, was singing over the thrum of the motor, perhaps out of exhilaration, perhaps out of boredom, or perhaps out of fear, though four years of war in Syria had dulled his sensitivity to risk and it had not been strong to start. The others were praying. O sea, be kind! the boy sang. “Shut up!” the others pleaded. Near the end of the crossing, with Turkey well behind them, the boat's motor gave out. The boy threw himself over the side of the rubber dinghy and began to flail his way toward the Greek shore, several hundred yards off; this was another mark of his heedlessness, as the water was cold and dangerously choppy. The others stayed in the boat.

A rescuer swam to the boy and dragged him to the beach, on the island of Lesbos. A nurse brought him to a nearby tent. “Okay, talk,” she said.

“What do you want to hear?” the boy asked. He was warm and dry now but not entirely certain who the woman was.

“I want to hear everything,” the nurse replied. His name was Paul, he said, and he was 16 years old. He was angular and trim, with ropy limbs and thick hands and a brow that ran across his face in a brooding crease. His eyes were black and deep-set, and there was something distant and inscrutable but immediately attractive about him, an air of slight deviousness. His speech was somewhat wooden, as if he had recently memorized certain details of his life, but the nurse found his story to be broadly credible. As a Christian in wartime Syria, he said, he had been repeatedly imprisoned by jihadists. He glanced at the nurse's hijab. “Maybe you're one of them?” he asked. The question was playful, but the boy had not expected that his first encounter in Europe would be with a Muslim speaking Syrian Arabic, and he was wary. “Are you crazy?” she said.

Padnos asked him what he believed to be the goal of the jihad in which he was fighting. “To take over the world,” the boy replied, matter-of-fact. Padnos must have given him an incredulous look, because the boy went on, smiling, “You think it's a little unrealistic, don't you?”

She was Syrian-Swedish, from Stockholm, and had come to assist the hundreds of thousands of refugees and migrants arriving on Lesbos that year. She would be returning home soon and offered to help Paul re-settle there. He made it to Stockholm ten days later, on October 9, 2015. The boy was very young, and going to Europe was mostly an adventure for him, with no pre-determined end point. He had been told of Sweden's reputation for generosity toward refugees, though.

One of the nurse's friends, a physician named Lina, took to the boy, and often invited him to visit her, her husband, Otto, and their three teenage daughters. (The names of Lina, Otto, and the boy have been changed.) Paul seemed to her “a very vulnerable, charming young man, somehow,” Lina said recently. “He has a way to know how to—how do you say?—push on the right buttons, from the beginning. To get you affected.”

Others found him unmanageable. The nurse had arranged for Paul to live with another friend, but the woman asked to have him moved elsewhere: His sleep habits, and his moods, were erratic. The social authorities assigned him to the home of an elderly woman, but he fled after just a few days. At a small center for refugee minors, Paul declined to consume anything but candy and cigarettes and began punching walls and fighting. Later, he broke open the head of a safety razor and slashed his wrist.

Lina had once been a psychiatric nurse. Paul's episodes were to her less daunting than they were painful to observe from afar. She and Otto discussed taking the boy in. In addition to their growing affection for him, and their sense of responsibility to the refugees arriving in their country, their marriage had been strained for several years and they wondered if such a project—in its simple urgency, in what they felt to be its purity—might be what Otto called a “platform” for a new start. In early December, once they had obtained the necessary approvals, Paul moved into the family's duplex.

They knew almost nothing of his past. He spoke too little Swedish to describe it in detail, but early on he and Lina began a habit of walking after dinner, wandering for hours beneath the streetlights, and over time she was able to make out the contours of his life. Paul came from Shadadi, a small city in the eastern desert that had been occupied by jihadists for nearly three years. He was the youngest of ten brothers, the rest of whom—with his parents and three sisters—remained in Syria. He had been imprisoned, it seemed, by both ISIS and Al Qaeda, as the rival groups fought for control of eastern Syria.