C49 Unknowingly performing a spell

"Leonid!" Stefan called expressionless, his aura was darkened. "To what do I own this invasion?"

'Where is Fiona?" Leonid ignores Stefan's question, I look at him, but I am standing right in front of him, why can't he see me? I don't understand, Stefan moves his gaze and looks at me, he too is surprised, probably wondering how come, he can't see me