They reached the edge of the Hollow Forge on the fifth day.
It was not a city, not in the way that Theron had understood cities. It was a mountain that had been hollowed out, its peak carved into the shape of a fist, its slopes covered in towers and spires and walls that had been built to withstand the wars of gods.
And the smoke that rose from its heart was black, thick, the smoke of a thousand forges that had been burning for a thousand years.
"There," his father said, pointing toward a gate that had been carved into the mountain's base. "The entrance. The third piece is inside."
They walked toward the gate, the Echo pulsing in Kaelen's pack, the marks on his chest burning with a heat that had nothing to do with the cold of the wastes. And when they reached the gate, it opened.
The tunnel beyond was long, dark, its walls lined with runes that glowed with the same sickly yellow light that had burned in Malkor's chest. Theron could feel the heat rising from the depths, could hear the clang of hammers on metal, the hiss of steam, the grinding of gears that had been turning for a thousand years.
And then they were in the forge.
It was vast, larger than anything Theron had ever seen, its ceiling lost in smoke and shadow, its floor a maze of channels that carried molten metal from the heart of the mountain to the forges that lined the walls. And everywhere, there were things that had once been men.
They moved through the forge, their bodies fused with metal, their faces hidden behind masks of bronze, their hands—if they could be called hands—shaped into hammers and tongs and blades. They did not look at Kaelen and Theron as they passed. They did not seem to see them at all.
But something saw them. Something that was waiting in the heart of the forge, where the fires burned hottest and the metal flowed like water.
"You came," a voice said, and it was the voice of grinding gears, of metal on metal, of something that had forgotten what it meant to be flesh and blood. "We were beginning to think you would not."
A figure stepped out of the shadows. It was larger than a man, its body a nightmare of fused flesh and twisted metal, its face a mask of bronze that had been welded to its skull. But there were eyes behind the mask, eyes that had once been human, and they were looking at Kaelen with something that might have been recognition.
"Malkor," Kaelen said. "I killed you. In the wastes. I tore you apart."
The thing that had been Malkor laughed, and the sound was the sound of grinding gears, of metal on metal, of something that had forgotten how to feel.
"You killed what Volkar made. What the Skylords built. But I am not Volkar's creation. I am something older. Something that was here before the Skylords came. Something that has been waiting for you."
It stepped closer, and the light of the forges caught its face, and Theron saw something that made his breath catch in his throat.
There was a symbol on its chest, carved into the metal, glowing with the same soft light as the Echo in his father's pack.
A Firstborn rune.
"You are the Forge-Keeper," Kaelen said. "The one who was here before the Skylords. The one who built the Echo."
"I am what remains of that one." The thing that had been Malkor raised its hand, and in its palm was a shard of crystal, pulsing with the same rhythm as the Echo. "I have been waiting for you for a thousand years, Kaelen. Waiting for the one who could wield what I made. Waiting for the one who could finish what I started."
It held out the shard, and the light of the Echo flared, reaching for it, hungry for it.
"Take it. Take the third piece. And become what you were always meant to be. The God-Killer. The Shattered Oath. The end of everything that was."
Kaelen looked at the shard, at the light that pulsed in the Forge-Keeper's hand, at the thing that had been waiting for him for a thousand years.
And he reached out and took it.