Seven hundred metres down, and the SM’s self-diagnostic program told it that a reflective cylinder in its laser had cracked. Twelve had expected this to happen, as there was no way of injecting crash foam, or even admitting seawater, into the cavity within the cylinder - and to do so would have screwed the optical perfection of the system anyway. The rate of its descent was also slowing in proportion as the density of the water increased. The drone dared not reverse its AG to pull itself down faster, as that would be too easily detected. Shortly it passed the heirodont, which was now thinner than it had been above, the water having compressed it too. The creature’s eyes glimmered from their pits as it turned and sculled hesitantly towards Twelve, but the drone was well past it before it could decide if this strange-looking object was animal or vegetable.

Now it was getting colder, and dark enough to necessitate Twelve switching from visual to low-intensity sonar, changing the emitted signal at random so that nothing constant could be detected. The Prador vessel lurking down here somewhere would be sure to have some kind of detection equipment out. A thousand metres down, and the lip of the trench finally came into sight. But Twelve did not bother to alter its course as it hit solid rock and, in a spray of silt, bounced over the edge. Using water jets, it corrected its tumble and studied the cliff face it was falling past. Down here, in weedy crevices, were whelks as big as houses riding on spreads of flat white tentacles; odd, diamond-shaped jellyfish adhered to clear surfaces, giving some expanses of rock the appearance of one great scaled beast; and long blue glisters hunting bulbous boxies that might easily be mistaken for soap bubbles. All very interesting, but all recorded and on file up on Coram. Twelve focused its attention downward, as the bottom of the trench floated up to meet it. It bounced in a cloud of silt and razor-thin shell fragments, then with great care extended the range of its sonic scans.