Butler nodded.

'Good. Now, there are several items you will need to procure for our moonlight jaunts.'

Butler scanned the sheet: basic field equipment, a few eyebrow raisers, nothing too puzzling until…

'Sunglasses? At night?'

When Artemis smiled, as he did now, one almost expected vampire fangs to sprout from his gums.

'Yes, Butler. Sunglasses. Trust me.'

And Butler did. Implicitly.

Holly activated the thermal coil in her suit and climbed to 4,000 metres. The Hummingbird wings were top of the range. The battery readout showed four red bars — more than enough for a quick jaunt through mainland Europe and across the British Isles. Of course, the regulations said always travel over water if possible, but Holly could never resist knocking the snowcap from the highest alp on her way past.

The suit protected Holly from the worst of the elements, but she could still feel the chill sinking into her bones. The moon seemed huge from this altitude, the craters on its surface easily distinguishable.

Tonight it was a perfect sphere. A magical full moon. Immigration would have their hands full, as thousands of surface-sick fairies were drawn irresistibly overground. A large percentage would make it, probably causing mayhem in their revelry. The earth's mantle was riddled with illegal tunnels and it was impossible to police them all.

Holly followed the Italian coast up to Monaco and from there across the Alps to France. She loved flying, all fairies did. According to the Book, they had once been equipped with wings of their own, but evolution had stripped them of this power. All but the sprites. One school of thought believed that the People were descended from airborne dinosaurs. Possibly pterodactyls. Much of the upper-body skeletal structure was the same. This theory would certainly explain the tiny nub of bone on each shoulder blade.

Holly toyed with the idea of visiting Disneyland Paris. The LEP had several undercover operatives stationed there, most of them working in the Snow White exhibit. It was one of the few places on earth that the People could pass unnoticed. But if some tourist got a photo of her and it ended up on the Internet, Root would have her badge for sure. With a sigh of regret, she passed over the shower of multicoloured fireworks below.

Once over the Channel, Holly flew low, skipping over the white-crested waves. She called out to the dolphins and they rose to the surface, leaping from the water to match her pace. She could see the pollution in them, bleaching their skin white and causing red sores on their backs. And although she smiled, her heart was breaking. Mud

People had a lot to answer for.

Finally the coast loomed ahead of her. The old country. Eiriu, the land where time began. The most magical place on the planet. It was here, 10,000 years ago, that the ancient fairy race, the De Danann, had battled against the demon Fomorians, carving the famous Giant's Causeway with the strength of their magical blasts. It was here that the Lia Fáil stood, the rock at the centre of the universe, where the fairy kings and later the human Ard Rн were crowned. And it was also here, unfortunately, that the Mud People were most in tune with magic, which resulted in a far higher People-sighting rate than you got anywhere else on the planet. Thankfully the rest of the world assumed that the Irish were crazy, a theory that the Irish themselves did nothing to debunk. They had somehow got it into their heads that each fairy lugged around a pot of gold with them wherever they went.

While it was true that LEP had a ransom fund, because of its officers' high-risk occupation, no human had ever taken a chunk of it yet. This didn't stop the Irish population in general from skulking around rainbows, hoping to win the supernatural lottery.

But in spite of all that, if there was one race the People felt an affinity for it was the Irish. Perhaps it was their eccentricity, perhaps their dedication to the craic, as they called it. And if the People were actually related to humans, as another theory had it, odds on it was the Emerald Isle where it started.

Holly punched up a map on her wrist locator and set it to sweep for magical hotspots. The best site would obviously be Tara, near the Lia Fáil, but on a night like tonight, every traditionalist fairy with an overground pass would be dancing around the holy scene, so best to give it a miss.

There was a secondary site not far from here, just off the south-east coast. Easy access from the air, but remote and desolate for land-bound humans. Holly reined in the throttle and descended to eighty metres. She skipped over a bristling evergreen forest, emerging in a moonlit meadow. A silver thread of river bisected the field and there, nestling in the fold of a meander loop, was the proud oak.

Holly checked her locator for life forms. Once she judged the cow two fields over not to be a threat, she cut her engines and glided to the foot of the mighty tree.

Four months of stakeout. Even Butler, the consummate professional, was beginning to dread the long nights of damp and insect bites. Thankfully, the moon was not full every night.

It was always the same. They would crouch in their foil-lined hide in complete silence, Butler repeatedly checking his equipment, while Artemis stared unblinking through the eye of the scope. At times like these, nature seemed deafening in their confined space. Butler longed to whistle, to make conversation, anything to break the unnatural silence. But Artemis's concentration was absolute. He would brook no interference or lapse of focus. This was business.

Tonight they were in the south-east. The most inaccessible site yet. Butler had been forced to make three trips to the jeep in order to hump the equipment across a stile, a bog and two fields. His boots and trousers were ruined. And now he would have to sit in the hide with ditchwater soaking into the seat of his trousers. Artemis had somehow contrived to remain spotless.

The hide was ingenious in design and interest had already been expressed in the manufacturing rights — mostly by military representatives — but Artemis had resolved to sell the patent to a sporting-goods multinational. It was constructed of an elasticated foil polymer on a multi-hinged fibreglass skeleton. The foil, similar to that used by NASA, trapped the heat inside the structure while preventing the camouflaged outside surface from overheating. This ensured that any animals sensitive to heat would be unaware of its presence. The hinges meant that the hide would move almost like a liquid, filling whatever depression it was dropped into. Instant shelter and vantage point. You simply placed the Velcroed bag in a hole and pulled the string.

But all the cleverness in the world couldn't improve the atmosphere. Something was troubling Artemis. It was plain in the web of premature lines that spread from the corners of his deep-blue eyes.

After several nights of fruitless surveillance, Butler plucked up enough courage to ask…

'Artemis,' he began hesitantly, 'I realize it's not my place, but I know there's something wrong. And if there's anything I can do to help…'

Artemis didn't speak for several moments. And for those few moments, Butler saw the face of a young boy. The boy Artemis might have been.

'It's my mother, Butler,' he said at last. 'I'm beginning to wonder if she'll ever — '

Then the proximity alarm flashed red.

Holly hooked the wings over a low branch, unstrapping the helmet to give her ears some air. You had to be careful with elfin ears — a few hours in the helmet and they started to flake. She gave the tips a massage. No dry skin there. That was because she had a daily moisturizing regime, not like some of the male LEP officers. When they took off their helmets, you'd swear it had just started to snow.