"Thank you for bringing this dastardly conspiracy to my attention. As your trusted mentor, I will make sure the plot is stopped and the evil-doers are brought to justice. You have fulfilled your objective! Just one thing...
"...who else have you told you were coming here?"
"Ah, my eternally loyal henchman. You have done well in following my orders without question. And now you shall get...EXACTLY what you deserve."
(Subverted delightfully in Dungeons & Dragons, a.k.a. THE BEST MOVIE EVER MADE.)