I reached across and put the window up on the passenger's side and got into gear and left the back end to dig for traction with the chains and then got a grip and moved off, going three blocks before I started playing with the gears and looking for patches of sand and using them for acceleration while the headlights fanned from side to side across walls and doorways and parked and stranded trucks, cars and carts and the characteristic bric-a-brac of the dockland environment, while the tracker fell behind for a minute or two before he saw I was onto him. His own lights began swinging across and across the mirror as he went into a series of slides and then got a grip and lost it and found it again and started to close up a little.

I chose a side street where the snow had piled into a drift against the wall of a warehouse and used it to get me through the ninety-degree arc, letting the rear end hit the snow and kick the Skoda straight again as I found traction in patches and put fifty yards behind me before the tracker's lights came flooding into the narrow street and threw my shadow ahead of me against the snow.

It happens. It happens sometimes: the director in the field sets up a model deployment of his shadow executive and his support group and his contacts and couriers and whatever he needs for a given mission, spinning his small and delicate network of resources and testing it out for strength and making changes where potential danger threatens, sitting back in his inner sanctum plugged in to his communications system with its portable scrambler and its bug monitor and taking signals from the shadow out mere and relaying them through the mast at Cheltenham to the signals board in Whitehall, the whole thing running like silk through a loom, and then one man and one man alone can suddenly send the web shaking because he's made a mistake, talked to the wrong people, exposed a password, missed the half-seen face in a doorway or the figure humped at the wheel of a parked car or the broken hair across a drawer in the hotel room, and the network becomes an alarm system and all we can do is shut down signals to prevent interception and get out of the safe-house before it's blown, run for cover, go to ground, hole up somewhere as the smell of the smoke starts drifting through the field where the fuses have blown and someone reaches for the chalk in the signals room in London and writes it up on the board: Mission compromised, clear all channels and stand by.

It was happening now.

The shadow of the Skoda was flitting across the snow and the buildings ahead of me like a bat out of a nightmare as both vehicles swung and corrected and swung again over the treacherous surface. There wasn't any question of pushing the speed to more than thirty or forty kph through streets like this with dead traffic all over the place, parked or abandoned or stuck in a drift; there was only a question of the leading car's ability to outstrip the one behind, and it was already becoming clear that whatever the tracker was driving it was more potent under the bonnet than the Skoda, possibly a Merc or a Porsche or a Mazda with tight suspension and a pinpoint steering system. All I could hope to do was let him close in and then try to fox him with tricks.

I kept seeing Roach, a short man with bright blue eyes and a round pink face, his fingers playing with each other as he transferred nervous tension, his nails bitten to pieces — I'd wondered about him when he'd shown us into the safe-house, but Ferris had told me he was totally reliable and had worked with him before. He wasn't a mole, Roach. He wasn't a changeling. We don't have any people like that, in the normal way of things, because the Bureau is conceivably the most elite intelligence organization in the western hemisphere, officially non-existent and responsible directly to the Prime Minister of the UK, and there are as many traitors in our ranks as there are in the SAS, whose number is reputedly sub-zero.

I didn't think Roach was a traitor. I thought he'd made a mistake. But in practical terms it didn't make a lot of difference: Meridian was in hazard.

Don't think about Roach. Think about survival.

The side street opened onto a major road and I touched the brakes, trying to get as much deceleration out of the drums as possible before they locked, but the speed wasn't coming down all that much and I'd have to do better than this because a truck was passing the end of the street and there'd be other traffic on the move and I didn't want to splash this thing all over the side of a heavy-duty haulage rig or anything else, for that matter, so I put the nearside front wheel into the deeper snow along the kerb and felt the drag and touched the brakes again but the surface was more or less pack-ice and we span full-circle and fetched up with the back end clouting a sand bin. That was all right because it brought the speedwell down and the major road was fifty yards ahead and it didn't look as if I still had enough momentum going to hit anything out there, but I was losing ground in terms of getting clear of that bastard and if I led him into the major road he'd overhaul me without any trouble because his car was out of an elite sports stable of some kind and the Skoda was made for taking the kids to school in comfort and running Aunt Gertrude home, so I did the only thing that was available to me and sighted him in the mirror and swung the wheel and bounced the Skoda against a drift and swung through a hundred and eighty degrees and gunned up and got smoke out of the rear tyres as they bit through the ice and reached solid tarmacadam and pushed the car back the way we'd been coming.

Part of the whole thing was going to depend on luck but I found enough steering to take the Skoda through the gap between the other vehicle and the sand bin — there was a lot of blinding light as we closed up and I think I heard a shout, he hadn't been expecting this and I suppose it worried him. We missed a total head-on thing but the sand bin was solid and the Skoda ricocheted to a certain extent and tore a door away from the other car and smashed quite I a lot of glass and I felt the sudden drag of deceleration and the Skoda [span half round and I saw the other car swinging much too wide and I much too fast, and one of the wheels came spinning past me as his front stub-axle sheared and he hit the wall of a building and bounced back and then went into a slow roll with the engine screaming and the bright red of a flame popping from inside the engine compartment as a fuel line was torn apart and a spark from the ignition found it.

The engine went on screaming until the fuel in the injectors gave out and then there was silence of a kind and when I hit my door open it raised an echo in the narrow confines of the street. He was still inside, the tracker, sitting there like a crash-test dummy with blood coming bright from a head wound, seeping across his face. Black smoke was rolling from underneath the car as spilled engine-oil took fire and I went for his seat-belt but it had snapped at the buckle so that was what the head wound was all about. I dragged him out of the car and across the snow and pushed him into the front of the Skoda on the passenger's side and got in and span the rear wheels to get the chains through the snow and finally got moving and started looking for cover as we drove, any sort of cover where I could pull up and talk to this man, I wanted information.

'Can you hear me?'

He didn't answer, just keeled over a bit, that was all, so that I had to push him upright again. I had time now to realize that his head was a mess and by this time most of his face was covered in blood. Lights washed across the buildings from behind but there'd be no traffic coming this way: the burning car was on its side and blocking the street.

'Can you hear me?'