Her expression showed no noticeable change when she heard Mephisto's plainly teasing question.
She withdrew her gaze from the corner where Kaecilius had vanished and rested it on Mephisto's eyes, burning with sulfur flame, for about two seconds.
"I am afraid." The Ancient One's voice came from where she stood. Its timeless, ancient calm remained unchanged, but now held a frankness as though she were answering a tired yet unavoidable question.
"I'm afraid Kamar-Taj will produce another traitor. I'm afraid Kaecilius will keep acting as an inside man for some other power out there. I'm afraid the man I spare today will become Strange's greatest threat tomorrow. I'm afraid of all of those things."
She paused, then changed tack:
"But Mephisto, you've lived through so many epochs. You should understand one thing better than I do: fear has never been a basis for making decisions.
"The real reason I let Kaecilius go wasn't that I feared him, or that I didn't. It was that keeping him here had no value for me, for Kamar-Taj, or for Strange.
"If I kill him, I get a dead traitor. If I release him, I get a living traitor who will continue exposing himself. And sometimes, a living traitor is more useful than a dead one."
Mephisto let out a snort of laughter.
"Ancient One, that certainly sounds impressive, but I can't help feeling you let Kaecilius go for more than his being 'useful.'
"Did you already know this would be today's outcome? Did you plan from the start to let Kaecilius escape, then leave him to slowly serve whatever purpose he still could in some corner out there?
"You already have enough debts to your name. One more reputation for 'sparing a traitor' really wouldn't mean much to you."
The Ancient One tilted