Besides, Janson knew this area; when he was at Cambridge, he’d had a friend who lived in the Marylebone neighborhood, and they had taken long strolls through the great verdant expanse, three times the size of New York’s Central Park. Some of it was overlooked by the neoclassical grandeur of Hanover Terrace, with its noble Georgian exteriors and creamy hues, the white and blue friezes adorning its architrave. But the park was a world unto itself. The waterways bustled with swans and odd, imported fowl; they were banked with concrete in some stretches while in others they lapped onto stands of marshy reeds. On the concrete walkway along the embankment, pigeons competed for crumbs with swans. Farther out, trimmed rows of boxwood provided a dense green border. A red lifesaver was mounted on a small wooden kiosk.

To him, it had always felt like a refuge, this vast campus of trees and grass, playing fields and tennis courts. The boating lake stretched like an amoeba, narrowing to a stream that, edged by flower beds, ran under York Bridge in the southern part of the park. And in the inner circle was Queen Mary’s Garden, filled with exotic flora and rare fowl, discreetly penned: a sanctuary for wild birds and lonely, fragile people. Regent’s Park, a legacy of the crown architect John Nash, represented an Arcadian vision of an England that, perhaps, never was—the Windermere in the middle of the metropole, at once artfully rusticated and carefully manicured.

Janson jogged toward the boating lake, past the trees, trying to clear his head and make sense of the astounding assault. Even as he ran, though, he was intensely alert to his surroundings, his nerves jangling.

Was it safe?

Was he dealing with a single sniper? It seemed unlikely. With such exhaustive preparation, there must have been flanking gunmen in place, covering different wings of the house, different exposures. No doubt, perimeter security was as exacting as Thwaite had indicated. But there were few local defenses against such long-distance marksmanship.

And if other snipers were in the area, where were they?

And who were they?

The intrusion of menace in this pastoral redoubt struck Janson as itself an obscenity. He slowed down and looked at the great willow tree in front of him, its branches drooping into the boating lake. A tree like that might be a century old; his eyes must have fallen on it when he visited the park twenty-five years ago. It had survived Labour governments and Tory governments alike. It had survived Lloyd George and Margaret Thatcher, the Blitz and rationing, eras of fear and of boisterous self-confidence.

As Janson approached it, the thick trunk suddenly revealed a rude patch of white. A soft, tapping noise: lead hitting puckered bark.

A shot that had missed him, again, by a matter of inches. The uncanny accuracy of a bolt-action sniper rifle.