Pilgrim Saltmire had arrived in Highwater Reach six years ago, with a trunk of clothes and books, and a case of fossils carefully packed in straw. It was the first time he had travelled outside the territory of his tribe. Thanks to his grandfather’s recommendation, the celebrated scholar Master Able had hired him as his personal secretary, and he’d been brimming with giddy anticipation and foolish optimism.

Master Able had first won fame while he had still been a pupil of Master Hopestart, the natural philosopher who advanced the theory of selective change, which explained that the vast variety of plants and animals had developed from simpler organisms by the slow, cumulative acquisition of new characteristics. It had been denounced as heresy by priests and philosophers who claimed that because the form of every species was a perfect realisation of the Mother’s will, no change was possible unless She desired it, and those changes were always accompanied by global catastrophe. The great flood which had destroyed the terror lizards; the cleansing fire which had put an end to the wickedness of ogres and left the narrow line of char found in sites all across the Union and United Territories; the plague which had turned bears into crazed beasts after they strayed from the right path. Master Able had been at the forefront of debates which had overturned those old beliefs, explaining the principles of selective change with devasting clarity, mocking the chop-logic of its detractors and famously saying that just as natural philosophy should not seek an explanation for the Mother, so religion had no business measuring the world. He had reinforced his status with his work on comparative anatomy, including studies of selective change in bears and the ancestors of people, but by the time Pilgrim became his secretary his reputation was greatly diminished, his health was failing and he had fallen out with many of his colleagues because of his interest in sightings of the visitors.