The invitation was felt and immediately piqued Loki's interest. This was no ordinary mortal that had done this, he could tell. However, he could also perceive this was not a personal extension, but a general summons. Ever since his arrival in Midgard, Loki made it his personal mission to seek out other sorcerers like himself in order to estimate their strengths, their weaknesses and where they aligned themselves. To know his possible enemies. This one who had called was new to the area and was quite powerful, therefore needed his attention.
Before leaving, he shape-shifted his form into that of an elderly woman; grey hair, wrinkles and a twinkle in her eye: completely harmless. He then withdrew his radiant, magical energy into himself so that it could not be so easily perceived. To one who was sensitive to magic, they would believe the innocent, old lady had some magical ability, but not a whole lot.
Loki did not realize that the mortal he was going to see was an exceptional case.
In a blink of an eye, Loki appeared at the doorstep of a brownstone. With her walking cane, he rapped upon the door and waited, smiling.