focusing her thoughts. "And now I think I know what it is."

"So tell me," Floyd said.

"The spheres form a single machine, as wide as Europe, one part of it in Paris, one part somewhere in

Berlin, another somewhere in Milan. But they're really all part of the same instrument. It simply has to be that big for it to work."

"And this instrument is what, exactly?"

"An antenna," she said, "just like the one on a wireless. Only it isn't radio waves it's set up to detect. It's gravity."

"And you figured all that out just by looking at that sphere?"

"No. I'm good, but I'm not that good. We use tools for measuring gravity in my work as well.

Sophisticated tools for peering through the ground, picking up the density changes caused by buried

structures. Needless to say, we had to study the theory of how these things work when we were being schooled up, and that meant going right back to the early history of gravity-wave detection."

"Maybe I don't read the right newspapers," Floyd said, "but I didn't know there was a history of gravity-

wave detection."

"There's definitely a history," Auger said, "but it isn't your fault that you don't know about it."

They had reached ground level. The ramp emerged in a narrow canyon formed by two long rows of

partially demolished buildings, still standing to their first or second storeys. Pipes, conveyors, conduits and catwalks threaded the s.p.a.ce over their heads.

"Tell me what I need to know."

"This isn't going to be easy for you to follow, Floyd."

"It'll take my mind off my headache."

"Then I have to tell you about s.p.a.ce-time. You ready for this?"

"Hit me," he said.

"There's an old saying amongst students of gravity: matter tells s.p.a.ce-time how to bend; s.p.a.ce-time tells

matter how to move."

"It's suddenly a lot clearer."

"The point is that everything we see is embedded in s.p.a.ce-time. You can think of it as a kind of rubbery

fluid, like half-set jelly. And since everything has a ma.s.s of some kind, everything distorts that fluid to one degree or another, stretching and compressing it. That distortion is what we experience as gravity. The Earth's ma.s.s pulls s.p.a.ce-time in around it, and the distortion in s.p.a.ce-time around the Earth makes things fall towards the planet, or orbit around it if they have the right speed."

"Like Newton's apple?"

"You're hanging in there, Floyd. That's good. Now let's move up a notch. The Sun pulls its own blanket of s.p.a.ce-time around it, and that tells the Earth and all the other planets how to move around the Sun."

"And the Sun?"

"Follows a path in s.p.a.ce-time dictated by the gravitational distortion of the entire galaxy."

"And the galaxy? No, don't answer that. I get the picture."

"You get half the picture," Auger said. "What we've talked about so far is a permanent bending of s.p.a.ce-

time around a ma.s.sive object. But there are other ways to bend s.p.a.ce-time. Imagine two stars swinging around each other, like waltzers. You got that?"

"Sure. I'm admiring the view as we speak."

"Make those stars super-ma.s.sive and super-dense. Make them whip around each other like dervishes,

spiralling in towards an eventual collision. Now you've got yourself a pretty fierce source of gravity waves. They're sending out a ripple, like a steady note from a musical instrument."

"I thought you didn't like music."

"I don't," she said, "but I can recognise a useful a.n.a.logy when it comes along."

"OK-so two stars circling around each other will give you a gravity wave."

"There are other mechanisms for producing such a wave, but the point is that there are a lot of binary

stars out there: a lot of potential gravity-wave sources dotted around the sky. And they all have a unique note, a unique signature."

"So if I pick up a tone-"

"You can work out exactly where it originated."

"Like knowing the flash pattern of a lighthouse?"

"Exactly that," Auger said. "But now comes the hard part. Somehow you have to measure those waves.

Gravity is already the weakest force in the universe, even before you start worrying about measuring microscopic changes in its strength. It's like trying to hear someone whispering on the other side of the ocean."

"So how can you do it?"

She was about to tell him when movement from above caught her eye: a glint of polished metal against

the low grey sky. There was just enough time to register the small figure crouched on one of the overhead pipes, and the nasty little weapon it clutched in one clawlike hand.

"Floyd..." she started to say.

The gun fired, making a rapid, high-pitched laughing sound. Auger felt a sudden warm pain in her right

shoulder, and then she was on the ground and the pain became worse. She was still looking up. The child stood balanced on the pipe, seemingly unfazed by vertigo. It held the gun aloft, releasing a sleek sickle-shaped clip from the grip and inserting another.

Floyd took out the automatic she'd given him. He thumbed off the safety catch and took a two-handed stance, squinting against the sky.

"Shoot the f.u.c.ker," Auger said, grimacing against the pain.

Floyd fired. The gun jerked in his hand, the bullet winging off the underside of the pipe. The child began

to lower its own weapon, taking careful aim.

Floyd emptied another two slugs into the air. This time they didn't hit the pipe.

The war baby toppled from its perch, shrieking as it dropped to the ground. Its thin little arms and legs

wheeled as it fell. It hit the ground, bouncing once, and then lay quite still.

It was a boy.

Floyd spun around, scanning the buildings for evidence of more children. Auger pushed herself up on

her good elbow, and then touched the wound in her shoulder. She pulled her fingers away. There was blood on the tips, but not as much as she had expected. It still felt as if someone was twisting a hot iron poker around in her shoulder. She reached around the back and felt more wetness under her shoulder blade.

"I think that was the only one," Floyd said, crouching over her.

"Is it dead?"

"Dying."

"I need to talk to it," she said.

"Hold it right there," Floyd said softly. "You've just been shot, kid. There are other priorities just now."

"There's an exit wound," she said. "The bullet went through me."

"You don't know how many went in, or whether they fragmented. You need help, and you need it fast."

She pushed herself up and then struggled to her feet, using her good arm for leverage. The war baby lay

where it had fallen, quietly gurgling in a pool of its own blood, its head twisted towards them. The eyes were still open, looking their way.

"It's the same boy," she said. "The one that stabbed the waiter in Gare du Nord."

"Maybe."

"I got a good look at its face," she said. "I know it's the same one. It must have followed us here."

She hobbled over to the boy and kicked its gun away. The head moved, swivelling around to keep her in

view. The mouth lolled open in a stupefied grin and blood drooled from the smoke-grey lips. The black tongue moved, as if trying to form words.

Auger pressed her foot down on the war baby's neck. She was glad she hadn't managed to snap the

heels off her shoes now.