So much is happening all at once. When Ignatius mentions he's unfamiliar with the magic, Strange decides that he can help with that. After all, he can see magic. He activates his third eye: the burns on his forehead, hand, and elbow outline themselves in an eye shape with magical fire as Strange quickly glances at his surroundings.

All he can see is the magic of the Athenaeum. Which, considering that they're in the damn library to begin with, is intensely unhelpful. This is stupid! Of course that's the only magic he could see!

He's scowling slightly as he looks over to Ignatius to tell him that, but the fae gets the word in first. Strange's expression shifts and he just looks downright pleased that Ignatius is trusting him to help and murder these troublemakers. "Of course, my lord," he simply responds. And then, barely even a second later, Strange lobs that fireball he's holding in Rita's direction.