THEY LEAPT FROM THE CAR in a blur, flailing their arms like madmen, each shouting the same single word over the wail of the approaching sirens. For a few seconds no one reacted. Then Gabriel drew a Beretta from the glove box of the car and the pedestrians recoiled in fear. It proved to be an effective tool, the fear. He drove the crowd away from the BMW, helping the fallen to their feet, while Keller desperately tried to evacuate a double-decker bus. Terrified passengers jammed the doorways front and rear. Keller tore them free and hurled them into the street like rag dolls.

Motorists traveling in both directions along Brompton Road had stopped to watch the commotion. Gabriel beat his fists on the windscreens of the cars and waved the drivers onward, but it was no use. The traffic was hopelessly snarled. In the back of a white Ford compact, a curly-haired boy of two was strapped tightly into a car seat. Gabriel clawed at the latch, but the door was locked and the child’s terrified mother, apparently thinking him a madman, refused to open it. “There’s a bomb!” he shouted through the glass. “Get away!” But the woman only stared back, uncomprehending and mute, as the child began to cry.

Keller had completed the evacuation of the bus and was hammering wildly on the windows of the HSBC bank. Gabriel lifted his eyes from the child and stared over the roofs of the motionless cars toward the opposite pavement. A crowd of bystanders had gathered outside Harrods. Gabriel ran toward them, shouting, waving his gun, and the crowd dispersed in terror. In the stampede a pregnant woman fell to the pavement. Gabriel rushed to her side and hoisted her to her feet.

“Can you walk?”

“I think so.”

“Hurry!” he shouted at her. “For your child.”

He thrust her toward safety and in his thoughts began to calculate how much time had elapsed since the text message had appeared on his BlackBerry. Twenty seconds, he thought, thirty at most. In that brief span of time, they had managed to move more than a hundred people from what would soon be the immediate blast zone, but cars still jammed the street, including the white Ford compact.

Shoppers were now streaming from the entrance of Harrods. Gun in hand, Gabriel herded them back into the lobby, shouting at them to take shelter deep within the building. Returning to the street, he saw that the traffic had not moved. The white Ford compact waved to him like a flag of surrender. The woman was still behind the wheel, paralyzed by indecision, unaware of what was about to happen. In the backseat the child screamed inconsolably.