How I Stole the Princess's White Knight and Turned Him to Villainy: The Complete Works

What's a white knight to do when his princess is causing utter havoc leading in mass murder? Go to the famous Black Sorcerer of Grimslock for help, apparently. What's a black sorcerer to do when the white knight comes to him for help? Keep him, naturally. Devan does not approve of this payment plan. Tan does.