This post contains lots of spoilers!!
Alexandria (or Lexi) has just essentially graduated and taken her assessment test. She's been dating her best friend and neighbor Byron. That's frowned upon until they get their assessment results because they could be placed in different levels. But they're both confident they'll place about the same or higher than their parents so it won't be an issue.
This book does one thing that I love that most dystopian novels don't do - she explained how we went from now to the society that exists in the book. Actually, I have a hard time even calling this dystopian. I think it was intended to be, but things seem mostly better than they are now. Society is structured into classes, which are represented by colors. How well you do on your assessment test determines what level you are placed into. So while you might have been raised in the lower class, if you do well enough on your assessment, you could be placed higher. Seems a fairer way to do it than we do now. There are definite income differences between the levels, but not like the massive income inequities that exist now. Anyway...
Lexi gets her results and she ends up with a gold level, the highest possible. She's been what they call fast-tracked. She's ecstatic and goes to tell Byron when she finds out he's been placed in orange, even lower than their parents' levels of blue (blue is solidly middle class, orange is definitely not). Byron and his family are angry at her because they think her father had something to do with it because there was some kind of incident at the plant/factory (I can't remember what kind of company it was) where they are both are managers.
Lexi is devastated for Byron and refuses to be happy for herself. They're so in love (although we never really see why they love each other except that they've known each other forever) and so she can't be happy when his life is now effectively over.
She flies to New York, where she will be attending college (only certain levels go to college and only fast-trackers are at her college). She meets a guy on the plane named Avery who takes her under his wing. She quickly becomes the teacher's pet, which annoys the other students. Her teacher renames her Zandria because Alexandria is too long and Lexi is too cutesy. Her teacher wants her to be a business owner or a politician's wife, but she is determined to become a politician herself so she can change things for the lower classes. This is one part of the book that really bothers me - apparently women, especially those new to fast track, are expected to marry into power. Luckily, that's not good enough for Zandria (good thing, otherwise I would have had to stop reading the book).
Avery invites her to parties and brings her into the vital social scene of the fast trackers. He explains the importance of power. At one of the parties she meets Autumn, typical mean girl, who takes a liking to her and they become friends, although Zandria knows that Autumn would be vicious if Zandria makes a wrong move. Avery wants to be more than friends, but Zandria's still in love with Byron, so she keeps politely turning him down. And in the dumbest of all coincidences, Byron ends up being a trash guy at the college (seriously? They couldn't find an orange level job for him closer to home? In any other part of the country? This is way too convenient). He's mean at first, but then he apologizes and she starts sneaking him food. She also takes on her own servant, who was being mistreated at a party by one of her fast-tracker "friends." Of course Zandria treats her more like a friend and roommate.
She makes a plan to take over businesses already owned by blue levels (because gold levels can take over any business owned by a lower level) to build up the money for a campaign. She beings opening nightclubs. After opening night she sees Byron out at a restaurant with another fast-tracker who is known to be gay. She assumes he's essentially sold himself to this guy and is horrified.
Thanks to some spying, she finds out that it was actually Avery's dad who was responsible for both Byron's low ranking and her high ranking. Apparently Avery's dad owns the company where her and Byron's fathers work. Avery had accompanied him to the plant/factory on a visit years ago and fallen in love with Zandria from afar. So he arranged for her to be fast-tracked and for Byron to be assessed lower so that he wouldn't be competition. Zandria hates Avery for this, but can't show it because she fears what Avery could do to her with all of his power in fast-tracker society. Avery just doesn't seem all that evil to me. He's definitely no hero, but he's essentially an entitled rich kid - not an awesome guy, but not pure evil the way that Zandria makes him out to be.
Avery proposes to Zandria and she agrees, but only if he'll change Byron's assessment. Avery is reluctant because he's afraid she'll still want to see Byron but she assures him she won't. He convinces his father to change Byron's level to purple (one above blue). So Byron is saved but now she's stuck marrying someone who she hates.