Excerpt from The Perfect Girl by Gilly Macmillan, plus links to reviews, author biography & more

We walk past my aunt Tessa, who's in charge of a camera that's been set up to record our performances. The idea is to replay them later, to analyze them for imperfection, and identify areas where improvement can be squeezed out of us.

Tessa is squinting a bit nervously at the camera as if it might turn around and lick her face, but she gives us a thumbs-up. I love Tessa; she's like a much more chilled-out version of my mum. She has no kids of her own and she says that makes me all the more special to her.

The other faces in the church smile as Lucas and I walk between them, creasing deeper into expressions of encouragement as we approach. I'm seventeen now, but I've known this look since I was a little child.

Mum describes these sorts of people as our "supporters." She says they'll turn up to watch time and time again if we play well, and they'll tell their friends. I don't love the supporters, though. I don't like the way they come up to you at the end of a concert and say stuff like "You have such a gift," as if piano playing isn't something that you work on day in and day out, if you want to make it perfect.

You can almost see the word "genius" flashing up like a neon sign in their minds, temptingly bright. Beware that sign, I would say to them, if they asked. Be careful what you wish for, because everything has a price.

In the front row of the church, the last pair of faces I focus on belong to my mum and Lucas's dad. Or, to put it another way, my stepdad and his stepmum, because Lucas and I are stepsiblings. As usual, they're wearing the too-bright expressions of parents who are disguising a level of ambition for their children that could choke you.

Lucas is ahead of me by the time we get to the end of the aisle and he's already taking his seat as I step up onto the platform where the piano sits.

We're going to start by playing a duet. It's a crowd pleaser, the brainchild of our parents. Plus, they think it'll help us to calm our nerves if we play together at the beginning.

Lucas and I would both rather play alone, but we humor them, partly because we have no choice, and partly because we're both performers at heart and a performer wants to perform, needs to perform, loves to perform.

A performer is trained to perform.

So we'll do it, and we'll do it as well as we can.

As I sit down at the piano, I keep my back straight and I'm smiling for the audience even though my insides have constricted and twisted so they feel like a ball of elastic bands. But I don't smile too much. It's important that I look humble too, that I get my performance face just right.

There's a bit of fuss while Lucas and I get settled and adjust the piano stools. We already know that they're perfectly positioned, because we tried out the piano before everybody arrived, but still we fiddle about with them, the spacing of them, a tiny height adjustment. It's part of the performance. It's nerves. Or showmanship. Or both.

Once we're both sitting perfectly, I place my hands over the keys. I have to work hard to control my breathing because my heart is hammering but my focus sharpens onto the music that's ahead, all of me waiting to hear those first notes now, like a starting gun at the beginning of a race.

The audience is hushed. Just a cough from somebody that echoes around the vaults and columns. Lucas waits for the sound to disappear and, in the absolute silence that follows, he first wipes his palms on his trouser legs and then he positions his hands over the keys.

Now that smooth run of black and white stretching out beneath our hands is everything and I watch his hands as intently as an animal ready to pounce. I mustn't miss his cue. There's a beat or two more of perfect silence before he arches his palms and his hands bounce lightly: once, twice, three times.

From The Perfect Girlby Gilly Macmillan. Copyright © 2016 by Gilly Macmillan. Reprinted by permission of William Morrow, an imprint of HarperCollins Publishers