It was Professor Solomon Rosner who sounded the first alarm, though his name would never be linked to the affair except in the secure rooms of a drab office building in downtown Tel Aviv. Gabriel Allon, the legendary but wayward son of Israeli intelligence, would later observe that Rosner was the first asset in the annals of Office history to have proven more useful to them dead than alive. Those who overheard the remark found it uncharacteristically callous but in keeping with the bleak mood that by then had settled over them all.

The backdrop for Rosner’s demise was not Israel, where violent death occurs all too frequently, but the normally tranquil quarter of Amsterdam known as the Old Side. The date was the first Friday in December, and the weather was more suited to early spring than the last days of autumn. It was a day to engage in what the Dutch so fondly refer to as gezelligheid, the pursuit of small pleasures: an aimless stroll through the flower stalls of the Bloemenmarkt, a lager or two in a good bar in the Rembrandtplein, or, for those so inclined, a bit of fine cannabis in the brown coffeehouses of the Haarlemmerstraat. Leave the fretting and the fighting to the hated Americans, stately old Amsterdam murmured that golden late-autumn afternoon. Today we give thanks for having been born blameless and Dutch.

Solomon Rosner did not share the sentiments of his countrymen, but then he seldom did. Though he earned a living as a professor of sociology at the University of Amsterdam, it was Rosner’s Center for European Security Studies that occupied the lion’s share of his time. His legion of detractors saw evidence of deception in the name, for Rosner served not only as the center’s director but was its only scholar in residence. Despite those obvious shortcomings, the center had managed to produce a steady stream of authoritative reports and articles detailing the threat posed to the Netherlands by the rise of militant Islam within its borders. Rosner’s last book, The Islamic Conquest of the West, had argued that Holland was now under a sustained and systematic assault by jihadist Islam. The goal of this assault, he maintained, was to colonize the Netherlands and turn it into a majority Muslim state, where, in the not-too-distant future, Islamic law, or sharia, would reign supreme. The terrorists and the colonizers were two sides of the same coin, he warned, and unless the government took immediate and drastic action, everything the freethinking Dutch held dear would soon be swept away.

The Dutch literary press had been predictably appalled. Hysteria, said one reviewer. Racist claptrap, said another. More than one took pains to note that the views expressed in the book were all the more odious given the fact that Rosner’s grandparents had been rounded up with a hundred thousand other Dutch Jews and sent off to the gas chambers at Auschwitz. All agreed that what the situation required was not hateful rhetoric like Rosner’s but tolerance and dialogue. Rosner stood steadfast in the face of the withering criticism, adopting what one commentator described as the posture of a man with his finger wedged firmly in the dike. Tolerance and dialogue by all means, Rosner responded, but not capitulation. “We Dutch need to put down our Heinekens and hash pipes and wake up,” he snapped during an interview on Dutch television. “Otherwise, we’re going to lose our country.”

The book and surrounding controversy had made Rosner the most vilified and, in some quarters, celebrated man in the country. It had also placed him squarely in the...