Meet Laurel. She's currently upset about going from being homeschooled her whole life at her parents' beautiful cabin to entering a public high school in a larger town (Crescent City). On the plus side, though, at least she meets a cute boy named David, who helps her with her dreaded biology homework. Laurel tells David that she was adopted, but he doesn't mind and accepts her despite her weird vegan eating habits.
Then Laurel discovers a lump on her back. It grows larger, and then one day it blossoms into a flower with beautiful petals, still attached to her back. Laurel hides the flower with blouse-y shirts and scarves, and the only person she tells is David. Since he's a science nerd, they take samples to analyze under his microscope, and he confirms that they're most definitely plant matter.
Laurel's parents meet with a guy named Jeremiah Barnes about selling their family land; he makes Laurel really uneasy for some reason. Laurel and her parents drive out to visit the cabin and clean up some leaves, and that's when Laurel meets Tamani, a guy her age with green hair and green eyes. He says he's like her—a faerie. This is all too strange so Laurel runs back to where her folks are at the cabin. Can't say we blame her.
Seriously freaked out, Laurel fills David in on this, and they figure out that she doesn't have blood in her, but rather a clear fluid. She also doesn't seem to need to breathe oxygen (which they find out by exchanging air while kissing). In order to help Laurel adjust to her new identity as a faerie, David invites her to the school's costume dance. She lets her back-flower show as part of her costume as a faerie, and this helps her feel good about herself.
The flower wilts and falls off just like Tamani had said it would, and Laurel decides to go see him for more answers. He tells her that there are four kinds of faeries (Winter, Fall, Summer, and Spring) and that she's a Fall faerie; they each have their own special skills, kind of like magic. He also tells Laurel that the faeries sent Laurel to her human parents in order to have her inherit the land, because it's important to faeries for whatever reason. That's when Laurel tells him that Barnes had put in an offer on the house—which, according to Tamani, is terrible news.
Laurel asks her mom to think about selling the house for another week before signing anything, but then Laurel's dad gets really sick, and is rushed to the hospital vomiting blood. Yikes. David is super-supportive of Laurel during this time, and Barnes shows up at the hospital and gets Laurel's mom to start filling out forms to sell the house, since now the family urgently needs money to cover the hospital bills. The sale will be finalized the next day.
Since she thinks something fishy is going on, Laurel gets David to drive her to the address listed on Barnes's business card. Barnes is inside with two really ugly dudes and some weird misshapen dog-person thing. The men capture the kids, and Barnes sends the two dudes to drown Laurel and David in the river so they can't spoil his plans. Luckily, though, Laurel and David can exchange breath underwater until they manage to untie the rocks dragging them to the river's bottom.
David and Laurel manage to drive to her family's place, where Tamani and other faerie sentries bind their wounds from the scuffle. Turns out Barnes and his people are trolls, who are enemies of the faeries. Tamani tells Laurel (over his buddy's objections) that this piece of land holds one of the gateways to Avalon, the homeland of the faeries, so if the trolls got their hands on the land, that'll be bad news.
Laurel and David go with Tamani to find Barnes, and Barnes shoots Tamani (not fatally) and gets away. They ferry Tamani back to the land to get healed, and Laurel meets a faerie elder, Jamison. He praises her for finding her way in the human world, and gives her a diamond to give to her mom in exchange for not selling the land, plus a potion to make her dad better.
Laurel makes it to the hospital in time to give her dad the potion before he dies from the trolls' toxin, and she also gives her mom the diamond, saying that they need to put the land into a trust in Laurel's name. The diamond will cover the medical bills and then some.
Laurel returns to the land to tell the faeries about the arrangement, and while she's there, Tamani reveals that he knew her before she was sent to the human world with her memories erased. He loves her and asks her to come with him to Avalon, but she has to stay and protect her parents, since now the trolls know who they are and might target them. Laurel says goodbye to Tamani (with a kiss) in order to return to her human life (and to David), but she knows she'll see him again.