Joker's Tower, which had been dominating the western sky, loomed up before him. He hurried forward.

See-Why had risen and bathed the slim pyramid in pink light. The mist had left the reed beds round the base but the apex, five miles above the sea, was lost in perpetual cloud. Dom pushed his way through the dry reeds until he was within half a metre of the smooth, milk-white wall.

He reached out gingerly.

Hrsh-Hgn had once, realizing vaguely that interminable lectures on planetary economics might not be palatable fare for a boy, smiled and switched off the faxboard. He had fetched his copy of Sub-Lunar's Galactic Chronicles and told Dom about the Jokers.

'Name the races classed as Human under the Humanity Act,' he began.

'Phnobes, men, drosks and the First Sirian Bank,' Dom rattled off. 'Also Class Five robots by Sub-Clause One may apply for Human Status.'

'Yess. And the other racess?'

Dom ticked them off on his fingers. 'Creapii are Super-Human. Class Four robots are sub-human, sundogs are unclassified.'

'Yess?'

'The other races I'm not sure about,' admitted Dom. 'The Jovians and the rest. You never taught me anything about them.'

'It iss not necessary. They are so alien, you undersstand. We share no common ground. Things humanity considers universal among self-aware races - a sense of identity, for example - are merely products of a temperate bipedal evolution. But all the fifty-two races so far discovered arose in the last five million standard years.'

'You told me about that yesterday,' said Dom, 'Sub-Lunar's Theory of Galactic Sapience.'

Then the phnobe had told him about the jokers. The creapii had found the first joker tower and, all else having failed to open it, had dropped a live nigrocavernal matrix on it. The tower was later found to be intact. Three neighbouring stellar systems had been wrecked, however.