In his novel Maskerade, Terry Pratchett both skewers and gives an homage to Phantom the musical. Christine is beautiful...and talentless. It is Agnes Nitt -- fat and dumpy, from Lancre and talented enough in all things magic to become a great witch -- who sings like an angel. So she takes off for Ankh-Morpork, under the assumed name of Perdita, and sings around before landing at the famous opera there.
As a chorister.
From Wikipedia:
Christine is eventually given a position in the chorus at the Paris Opera House (Palais Garnier). She begins hearing a beautiful, unearthly voice which sings to her and speaks to her. She believes this must be the Angel of Music and asks him if he is. The Voice agrees and offers to teach her "a little bit of heaven's music". The Voice, however, belongs to Erik, a physically deformed and mentally disturbed musical genius who was one of the architects who took part in the construction of the opera. He is in love with Christine. He has also been extorting money from the Opera's management for many years, and is also called the "Opera Ghost" by the denizens of the Opera.
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Well, as a chorister UNTIL management offer Agnes the chance to sing Christine's role (b/c Christine basically can't sing her way out of a paper bag, pardon the cliche). She says yes, of course.
But the phantom knows who's singing for whom. And he offers Agnes secret lessons at night, wherein he proves to be a brilliant, if masked, talent.
Meanwhile, there has been a series of murders at the opera, and the phantom, of course, is the major suspect. So Agnes is trying to figure out who it is. She will eventually get some help from Nanny Ogg and Granny Weatherwax -- two witches who need no introduction if you have read any Discworld novels.
By the time it's all sorted out, Agnes has proven that the masked phantom was innocent of all murderous impulses: indeed, poor Walter was innocent of much thinking:
Walter's face was an agony of indecision but, erratic though his thinking might have been, it was no match for Nanny Ogg's meretricious duplicity. He was up against a mind that regarded truth as a reference point but certainly not as a shackle. Nanny Ogg could think her way through a corkscrew in a tornado without touching the sides.
And now, total spoiler alert if you want to read Maskerade:
It's set in an opera house, right? and they play operas, right? and nobody has ever heard of musicals in the American genre...
Nanny Ogg turned slowly. Her experience of opera had not been a lengthy one but witches pick things up quickly and there was the winged helmet worn by Hildeabrun in The Ring of the Nibelungingung, and here was the striped pole from The Barber of Pseudopolis, and there was the pantomime horse with the humorous trapdoor from The Enchanted Piccolo, and here...
...here was opera, all piled in a heap. Once the eye had taken it all in, it had time to notice the peeling paint and rotting plaster and the general air of gentle moldering.
snip
There was something like a desk in the tiny area of floor not occupied by the props. And then Nanny realized that it had a keyboard and a stool, and there were neat piles of paper on top oif it.
Walter was watching her with a big, proud grin.
Nanny ambled over to the thing. "It's a harmonium, ain't it? A tiny organ?"
"That's right Mrs. Ogg!"
Nanny picked up on of the sheaves of paper. Her lips moved as she read the meticulous copperplate writing.
"An opera about cats?" she said. "Never heard of an opera about cats...."
She thought for a moment, and then added to herself: But why not? It's a damn good idea. The lives of cats are just like operas, when you come to think about it.
She leafed through the other piles. "Guys and Trolls? Hubward Side Story? Miserable Les? Who's he? Seven Dwarfs for Seven Other Dwarfs? What're all these, Walter?"