And suddenly Artemis froze. In the middle of a heaving intersection.

Butler glowered at the three lanes of city traffic, a hundred impatient drivers leaning on their horns.

'I feel something,' breathed Artemis. 'Electricity.'

'Could you feel it on the other side of the road?' asked Butler.

Artemis stretched out his arms, feeling a tingle on his palms.

'He's coming after all, but several metres off target. Somewhere there is a constant that is not constant.'

A shape formed in the air. From nothing came a cluster of sparks and the smell of sulphur. Inside the cluster a grey-green thing appeared, with golden eyes, chunky scales and great horned ears. It stepped out of nowhere and on to the road. It stood erect, five feet high, humanoid, but there was no mistaking this creature for human. It sniffed the air through slitted nostrils, opened a snake's mouth and spoke.

'Felicitations to Lady Heatherington Smythe,' it said in a voice of crushed glass and grating steel. The creature grasped Artemis's outstretched palm with a four-fingered hand.

'Curious,' said the Irish boy.

Butler wasn't interested in curious. He was interested in getting Artemis away from this creature as quickly as possible.

'Let's go,' he said brusquely, laying a hand on Artemis's shoulder.

But Artemis was already gone. The creature had disappeared as quickly as it had come, taking the teenager with him. The incident would make the news later that day, but strangely enough, in spite of the hundreds of tourists armed with cameras, there would be no pictures.

The creature was insubstantial, as though it did not have a proper hold on this world. Its grip on Artemis's hand was soft with a hard core, like bone wrapped in foam rubber. Artemis did not try to pull away; he was fascinated.

'Lady Heatherington Smythe?' repeated the creature, and Artemis could hear that it was scared. 'Dost this be her estate?'