Pilgrim told her that it was an interesting story, but seemed to be based on the assumption that two strange and unexplained phenomena were related, and she said that if it was no more than a story it was a better one than Foeless Landwalker’s. Firestar was more like the Mother than Morningstar, which was hot and wet and permanently shrouded in cloud: a world of steaming oceans and jungle swamps that in no way resembled Foeless Landwalker’s fanciful descriptions of a paradisiacal garden, and an unlikely home for an advanced civilisation. Even so, she knew very well that ideas about life on Firestar were controversial. She and her friends had been relentlessly criticised by other skywatchers in the Invisible College, who pointed out that every person who claimed that they had seen canals had drawn a different map, that the seasonal shrinkage of the icecap at the north pole of Firestar was much less than that required to fill a planet-spanning network of waterways, and occultations of stars passing behind Him showed that His atmosphere was much thinner than the Mother’s, almost certainly too thin to support any life more complex than lichens and algae.

‘Our critics don’t understand that the canals are at the very limit of the resolution of our telescopes, and are also affected by fluctuations in the Mother’s envelope of air,’ Fragrant said. ‘Also, their calculations about the size of the icecap are speculative, and Firestar’s inhospitality is an important part of our theory: it explains why His inhabitants expended so much labour on building their canals. His atmosphere may be too thin to support animal life at this present time, but could have been much thicker when its inhabitants arose. They may have retreated to sealed underground cities, but certain kinds of plants should be able to grow on the surface, causing the seasonal changes that we observe. And if the original atmosphere of Firestar was different to that of the Mother, it would explain the appearance of the visitors – they may be wearing some kind of diving apparatus that contains air more suited to their physiology.

‘But these arguments miss the point, which is that this kind of speculation usefully tests the limits of possibility. Your master took a brave risk when he decided that sightings of the visitors were a worthy subject of study, but tried to apply traditional principles to a problem that cannot be understood by collecting and cataloguing facts. If we are to fully embrace the world in all its glory and mystery we must find new ways of seeing and thinking. You’d do well to remember that, when you meet Foeless Landwalker. You should open your mind. Purge yourself of prejudices and preconceptions. I don’t mean that you should believe everything, but you should not dismiss anything out of hand, either. No matter how strange or absurd it may seem.’