They had reached the bottom of Great Tower Street and were nearing the Tower of London. Flags waved from the turrets of the White Tower, backlit dimly against the last fitful gleams of the setting sun. Magnus nimbly avoided a group of tourists with box cameras and steered James down Tower Hill, a hand on his shoulder.

James lowered his voice, though the others were a distance away. Matthew, who was carrying the Pyxis, had stopped to point out something about the Tower to Cordelia. “What do you mean?”

“You know that there are other realms,” said Magnus. “Other worlds than this.”

Think of the universe then as like a honeycomb, each of its chambers a different realm. So some chambers lie next to one another. “Demons come from them, yes. They travel through the dimensions to reach our world and others.”

Magnus nodded. “There are some worlds ruled by demons, usually Greater Demons. Those worlds can be imbued with the very essence of those creatures. The dirt you gave Henry comes from one such place. A dimension under the power of the demon Belphegor.”

“Belphegor?” The name was immediately familiar. “He’s one of the Princes of Hell, isn’t he?”

“I know what you’re thinking about,” said Magnus, tapping his walking stick against the cobblestones. “Jem also contacted me about you. All roads lead to James Herondale these days, it seems.”

James rubbed his cold hands together. The wind off the river was sharp. “Jem contacted you?”

“About your grandfather,” said Magnus. “He told me that he was a Prince of Hell.” He glanced at the darkening sky. “You are wondering now if it might be Belphegor because the realm that you visit belongs to him.”

“Wouldn’t that make a kind of sense?” said James.

“It might. It might mean nothing at all. I can tell you that there is no record of anyone sighting Belphegor in more than a century.” Magnus hesitated. “Jem told me you were desperate to know who your grandfather is. My own father is a Prince of Hell. They are dark angels, James. Intelligent and cunning and manipulative. They bear the knowledge of thousands of years of life. Like angels, they have seen the face of the divine, but they turned away from it. They have chosen darkness, and that choice has reverberated through eternity. They cannot be killed, only wounded, and no good can come from knowing a Prince of Hell. They can never cause you anything but sorrow.”

“But wouldn’t it be better for me to know—”

“I summoned my father once. It was the worst mistake of my life. James, you are not defined by this—by this blood in you. I have found no trace, no hint of who your grandfather is, and I advised Jem to cease looking. It does not matter. You are who you are, made by the sum of your choices and actions. Not a teaspoon of demon’s blood.”