The room itself was smarter than Thaxa’s cistern – smaller, the walls better cut, presumably older. Halfway along the wall there was a kind of shrine, cut into the growstone, supporting two urns, side by side. Writing was neatly etched into plaster around the alcove with the urns, and Crimm, despite the bodies all around him, lifted his candle to see. These were the remains of Milaqa and Qirum, he read. Doomed by love and ambition . . . Milaqa was a heroine as great as Ana or Prokyid, but none must ever know the truth of their story . . . Milaqa. He remembered something about that name. The Black Crime. Oddly, in a room full of corpses, the etched words made him shiver. The Wall was very big and very old and none knew all its secrets. He hurried on.

Beyond the far door was a corridor, then another door marked with Ayto’s sign, and still another corridor. He was heading almost directly away from the Wall’s landward face, as far as he could tell. Ayto had been unimaginative and dogged in his choice of directions. But this corridor ended in a rectangle of blue light, pale, cold, clearly daylight. Crimm hurried on. The air grew increasingly cold, and there was slick ice on the growstone under his feet.

He reached the exit. A door, heavy, very ancient, its outer surface crusted with long-dead barnacles, lay open, revealing brilliant light that dazzled his dark-adapted eyes. He stepped forward cautiously, under a pale blue sky. He was outside the Wall, in its shadow. He was standing on a rough ledge of growstone, matted with green-brown fronds of dead seaweed, coated with ice. The Wall towered above him, a rough-finished surface deeply pitted and shining with rime. The sea lapped at the growstone ledge, covered with sheet ice that spread to a knife-sharp horizon, crisp and white. There were ice blocks piled up at the sea’s edge, perhaps a relic of the tides.

Somebody sat on the ice, cross-legged, beside a disc of dark blue, a hole in the ice. There was an animal beside him, inert, the head blood-splashed: a seal.

Crimm stepped forward carefully, and found himself standing on sea ice that creaked, a little ominously, reminding him of the end of the Sabet. He saw a place where the ice looked a little darker, a little bluer – older. He stepped that way. Rope sections had been fixed to the soles of his boots, and he could walk without slipping, if he didn’t rush.