Aliens have kidnapped your best friend.

At least that’s what it seems like. The two of you used to do things together all the time. You’d hang out, watch TV, shoot hoops or climb trees. You liked the same things and you knew each other’s secrets.

But now, sometimes, you feel like you barely know her any more. She never wants to do the things you used to do, and everything’s different. It’s almost like your best friend got kidnapped and replaced with someone who just looks like her.

In the new book, “Planet Middle School” by Nikki Grimes (c.2011, Bloomsbury Kids, $15.99 / $18.50 Canada, 155 pages), 12-year-old Joylin knows the feeling. Both her best friends are acting weird.

Joylin really hates it when people call her a tomboy. But what else can be said? She dresses in navy and baggy jeans, she’s got a killer jump shot, and she hates girly things. Her dad is secretly happy about it all. Her mother just rolls her eyes.

Yep, Joylin hates being called a tomboy, but she doesn’t mind when her best friend KeeLee teases her about sports and her lack of fashion sense. They’ve been BF’s since they were 9 and they’ve always done everything together… until middle school started.

When Joylin tried out for the basketball team, KeeLee joined the school choir. They don’t have the same classes very often. Sometimes, they don’t sit together in the lunch room any more, and that makes Joylin sad.

It makes her even sadder when KeeLee starts boy-watching.

And speaking of boys, even Jake, Joylin’s best male friend, is acting weird now that they’re all in middle school. He treats Joylin like a girl instead of like a friend, instead of the way he used to when he didn’t notice things like the bumps on her chest. Those bumps interfere with her jump shots, and she hates them.

Then a new boy shows up on the court one day. He smiles at Joylin and things change even more. How can she get Santiago to see her? Would a skirt and heels make him notice? Would makeup make a difference? And would Jake stop being such a jerk about this whole thing?

Why can’t things just go back to the way they were?

Remember how hard it was to stand with one foot in childhood and one foot in Grown-Up Land? Author Nikki Grimes brings all that confusion and those mixed feelings to life in this perfect little novel.

Using free-form story-poems of different lengths, Grimes gives voice to a smart young character who is also wise beyond her years. Joylin is a loyal friend, a good daughter and a thoughtful big sister, but she’s staring at a future that she’s not sure she likes. I enjoyed how we’re able to really get to know this character, and it would be fun to see more books with her in them.

Though there’s no reason a boy can’t read this book, I think 11-to-14-year-old girls will like it much better. For them, “Planet Middle School” is out of this world.