The agent scrutinising the monitor suddenly stiffened. He put a hand on his colleague’s shoulder and shook him. Otterman went over and looked at the monitor. The picture was fuzzy but there was no mistaking the figure of a man kneeling in front of a desk, his eye pressed to a telescopic sight. Otterman could see that the man was preparing to fire – there was no time to call for back-up. He slid his automatic from its leather shoulder holster and signalled for the two rookies to stand to the side.

Joker watched the two Secret Service agents head down the aisle towards Mary Hennessy, and saw her fumble for whatever it was that was hanging from her belt. He heard one of the agents reporting that she was reaching for something and then he heard another voice giving instructions to a sniper. Off to his right he heard the crack of a high velocity round and then Hennessy staggered back, one hand clutching at her chest. A red stain appeared on her usher’s shirt, and it reminded him of his days in the paintball arena in London. It was a perfect hit. This was different, though, and he knew Hennessy wouldn’t be getting to her feet and complaining about being taken out of the game.

She fell back and sat down heavily on the stairs. Joker could see that her eyes were wide open as if surprised, and the hand on her chest was twitching spasmodically. A blonde woman in a blue jacket rushed by the agents and knelt at her side.

Joker panned across to the office blocks, trying to see where the sniper was. It had been a good, clean shot. As he scanned the sky something passed across his vision, something large and white with the name of a Japanese electronics company on the side. It was so unexpected that Joker thought that he’d seen an advertising hoarding at the far end of the stadium, but then he saw wispy white clouds and knew that he was still looking up high, above the buildings. He took the binoculars away from his face and shaded his eyes with his free hand, gritting his teeth as pain from his shoulder lanced across his back. It was an airship, hanging in the sky more than a mile away. He frowned as he remembered what Cole Howard had told him about the long shot, the sniper who was planning to shoot the President from two thousand yards away, and how there was nowhere the sniper could make the shot from in Baltimore.

He let the binoculars hang on their strap around his neck and spoke into the radio again. His earpiece was buzzing with agents calling in situation reports following the shooting of Mary Hennessy. “Howard, are you there?” he asked, interrupting the agents.

“Is that you, Cramer?” It was Howard’s voice.

“Yeah. Have you seen the blimp?”

“Blimp?”

“The blimp. The airship. Over the city.”