Howard understood why she’d been embarrassed. She’d told her husband about the video, and was now worried she’d breached security. He wanted to tell her that it was okay, but he didn’t want to interrupt her. Her eyes were shining with enthusiasm. “You work out the heights of the towers, you calculate the angles and distances to the target, and then you superimpose that model on all the different venues where the target is due to appear.”

Howard tapped the file with his fingers. “He could do that?”

“He could do the preliminary work, sure. I haven’t shown him the video, but if I did he could put together the model, he said. He’d need to know the exact time of day the video was shot, so that he could use the shadows to determine heights and so on, and he might have to go out to the site to make some measurements, but yes, he could do it.”

“What about the venues? How would he get those into his computer?”

“You’d need street plans and the heights of the various buildings. He could customise a program for you, but it would take a lot of work to input the information. Once it’s in, though, the program would produce a 3-D model of the area, and it could then superimpose the snipers and target on it. It would tell you if the snipers were preparing for that venue or not. And if the models do fit, it’ll tell you exactly where the snipers will be. It’s a brilliant idea.”

Howard smiled. “It is. Your husband’s a very clever man. We do have one problem, though. At the moment we don’t know who the target is.”

Bonnie’s mouth opened, showing perfect white teeth. “Oh. I just assumed . . .”

“That it was the President?”

She nodded. “You think it’s someone else?”

“Bonnie, we just don’t know. But your husband’s idea is a good one. We know the President’s itinerary well in advance; if he can set the program up for us, I can bring in extra manpower to do the inputting.”

“So I can tell him to go ahead?”

“Sure.”

Bonnie positively beamed. “He’ll be so pleased. He thinks it’ll be like a detective story. He suggested I ask you to come to dinner with us, tonight. I’ll cook, and he can go over the details with you.”

It was an offer Howard couldn’t refuse.

Andy and Bonnie Kim’s house was a spacious single-storey ranch house in a quiet suburban road to the north of Washington. The grass was neatly cropped, the paths were edged with orderly flower beds and the Stars and Stripes fluttered from a white flagpole. Two cars were parked outside when Howard arrived: a Buick Roadmaster and a Cherokee Laredo, and when Bonnie Kim opened the front door and let him in he could see that the interior was just as all-American. It wasn’t what Howard expected at all. He’d always assumed that Koreans stuck closely to their heritage, but the Kims seemed to want it made clear to everyone that they were Americans through to the core.