Imagine each number has a color. Cool, right? For Mia, though, this isn't just a fun way to think about numbers; it's reality. And it makes math class super tricky. If she doesn't match the right colors with numbers, she has a hard time adding or subtracting—and you can go ahead and forget about multiplying.
Mia figures this is how everyone sees the world, but one day in math class, after she's laughed at and called a freak, she figures out that it's actually only her. She quickly learns to keep her mouth shut about the colors she sees in numbers and sounds.
Keeping her secret becomes increasingly hard after she fails a couple math tests as a teenager, though. She finally fesses up to her parents about what's going on, and they take her to see a doc. After a couple appointments and about a zillion questions, Mia learns she has synesthesia, which means she basically perceives things in two ways (instead of just one).
Mia's colored hearing and numbers stops feeling so strange once she meets a bunch of other synesthetes. Takes one to know one, you know? Soon she starts spending more time emailing Adam, a fellow synesthete, than she does hanging out with her BFF Jenna.
Mia dives into the process of exploring her synesthesia. She finds she'd rather try new techniques to enhance her colors (like acupuncture and bubble baths) than she would listen to Jenna talk about her birthday party plans, and she even goes to a synesthesia event where a bunch of other synesthetes talk about their experiences. Mia is loving it—she finally feels like she belongs, especially when Adam kisses her. Understandably, Jenna gets annoyed and the two girls grow apart. Oh, and Mia's still struggling in math class.
But Mia has even bigger problems than flunking math and losing her bestie. Her beloved cat, Mango, seems more tired and sluggish every day. And then Mango dies. Mia's heartbroken. She blames herself for being too preoccupied with her condition and not focusing enough on her cat. Of course her parents explain that it's not her fault, but still, she feels bad. Luckily, Jenna is there for her—she doesn't care about how distant they've grown in the last few months. Mia realizes she has a real friend.
On the flipside, Adam doesn't care all that much about Mango dying. In fact, he doesn't see what the big deal is. Mia is super hurt and vows not to be around him anymore. Synesthete or not, he's clearly not on her level.
Mia starts slowly getting back to normal when she learns that Mango has a bunch of kittens at the neighbor's house. Her brother, Zack, wants them to get one, but Mia's not so sure. That night, though, she has a dream about her family and knows she has to get the little kitten. Aw.