How do you get sorcery dog in Fable 2?

In Fable 2, to obtain the Sorcery Dog, you need to complete the "The Spire" quest. After finishing the quest and before leaving the area, look for a glowing ball of light (a "Demon Door") near the entrance. Interact with it, and it will reveal the Sorcery Dog, which you can then adopt. This unique dog has special abilities related to magic.