The Cryptic

I can always hear your angelic voice and the tune of the piano every time I passed by the music room in the middle of the night. But every time I get inside the room...

All I can see is nothing.

I always have these questions in my mind like, "who are you?", "what are you always doing in the music room every night?", "why can't I see you when I get inside that room?", "why do you want to be so mysterious?"

But the problem is, how can I asked those questions of mine if I don't even know how to find you?