It was the year Harry turned 18 that he decided to work in theatre. Granted, he had absolutely no talent in regards to singing, dancing or managing a performance, but he was a solid violinist, and was a genius with special effects and staging.
It was a muggle opera house (did wizards even have operas?) and he was fine with that. He would be out of place in the Wizarding World anyway. Hogwarts overlooked him, and he never cared to correct that mistake as he wanted no part in their little school anyway. Of course, this meant everything he knew about magic came from his parents and Tom. He didn't think anything more than basics were necessary when, as mentioned above, he planned on fully integrating with the muggles.
He was about six months into the job, already bored with all the similar sounding music and patronizing actors when he heard him. He brushed it off as a coincidence the first two times, but it was past reasoning now. Either he was going crazy or his some form of his father was calling out to him.
John was a good father up until he left. Even then, Harry could understand some way or another why he did it. He convinced himself he had moved on, didn't care anymore, tried to ignore the implications of him working in an Opera House of all things, but hearing his voice was a hit to the head. Like trying to rebuild a home in his mind that had been destroyed long ago brick by brick only to have it collapse at the utterance of a single word.
The voice was ghostly and high, but indisputably masculine.
"Father?" He wandered the hallways searching for the owner of the familiar, altered tone. Memories of hot afternoons in a small island crushed him like a stampede. Emotions he had been suppressing as skillfully as one could without the use of occlumency resurfaced.
"This can't be real." Harry thought, "It has to be a joke set up by Nellwyn Granger or something! The lead singer does seem to have it out for me, she had since I proposed replacing singers with humanoid machines that could hit every note with ease instead of risking the actors making mistakes and- You know, maybe her not liking me was a little justified. But still, I didn't think she'd do something so cruel, how would she even know what my dad sounded like?"
He reached an abandoned dressing room. It was fairly small, had a vanity with a small mirror, some chairs and dusty props here and there. It was dimly lit and altogether unimpressive. Still, there were candles, and that meant someone was here recently.
"Father, where are you?"
"My son, I am everywhere. I am in the walls, I am underground, I am the very words you speak, forever observing you. I am your Angel of Music"
Harry recalled the stories his father told him when he was teaching him how to play the violin. About an angel who wrote music than would seduce every listener. The kind that drove men to madness and inspired genius. The music that directly opposed the light-hearted garbage Harry heard every day in the Opera House.
The Music of the Night
Henceforth, father and son were reunited. Harry worshiped his father, agreed with all his creative choices and together they made music. Music that was unlike anything heard ever before. It was intimate music, the kind neither had any wish to share with the world. On some days, Harry would even work on his machines, ask his Angel of Music for advice on how to improve them.
Such were their lives for months, both quite content. However, night must end and bring forth a new day for better or worse. In this case, the day brought forth Tom Marvolo Riddle.