Rebel Belle by Rachel Hawkins

It's Homecoming night at her expensive Alabama private school and Harper Price is expecting nothing more than to dance with her friends and be crowned Homecoming Queen. As she is touching up her makeup for the big announcement, one of the school janitors, Mr. Hall bursts in bloody and dying. As he dies, he kisses and her Harper feels something cold going through her body, and suddenly feels stronger than ever. Mr. Halls last words to Harper are that he is sorry, and he asks her to please "look after him." The bathroom door explodes and her history teacher Dr. DuPont bursts in wielding a scimitar and threatening to murder her. They fight, and Harper is barely able to escape by stabbing Dr. DuPont in the throat with one of her stiletto heels. 

Harper is traumatized and runs out of the bathroom, and directly into the boy's bathroom where she vomits. She is, sadly, helped by her least favorite person in the world: David Stark, a guy she has hated since kindergarten. Harper expects David to freak out when he sees the gaping hole where the girl's bathroom door used to be, but is shocked when they walk into the hall and there is no sign of a struggle. Harper is so freaked out that when she learns she has been crowned Queen, all she can do is cry. Of course, her friends think it's because she is so happy to have won.

By the time she gets home, Harper is pretty much sure she hallucinated the entire event, except that she realizes her skirt is ripped, and still feels weirdly strong. She decides she has to try and see if she really has changed somehow, and tries to jump over an 8-foot fence, assuming she fall on her butt. She discovers she is not only able to almost clear the fence, but she is also extremely flexible and much stronger than before. She tries Googling around for some more information that might help her, but can't find anything on Mr. Hall or Dr. DuPont. She does, however remember Dr. DuPont using the work "Paladin" when he fought her, and she discovers that a paladin is a noble defender, which Harper thinks is dumb.

Based on her binge-watching a ton of super hero movies, Harper decides that in just about every case, someone eventually comes by to tell the hero what he is supposed to be doing, so she decides to just act normal until someone shows up. However, this proves hard to do when she arrives at school and sees that David Stark has written a story for the school paper about how she was puking her guts out in the boys room at Homecoming. She confronts David and he makes her so angry she tries to slap him, but finds that she is physically incapable of striking him, no matter how hard she tries. Harper assumes this is because if she really is a paladin, she must be the protector of her whole school, so she tries to slap her best friend's slightly obnoxious boyfriend Brando, and finds she can do it, no problem. She then tries to hit someone else, to further test the theory, and when she IS able to hit them, it dawns on her that the only person she cannot seem to hit is David. 

This theory is completely confirmed later that day when Harper's boyfriend Ryan confronts David about the article tries to push David in front of Harper. Harper goes full beast mode and beats up Ryan without being able to control her response. She runs away, but David follows her in his car, when they are both attacked by someone driving a black car. A car chase ensues and Harper is able to get the black car to crash into her family's pool. Just as David and Harper are trying to figure out how to explain the colossal damage to her parents the car and all the damage it caused vanishes and everything is returned to normal.

The next day Harper tries to explain to David what she knows about what has happened, and he tells her that he has no idea why people would be trying to kill him or why he would need protection, but that he thinks some of his dreams may be prophetic, and he has never understood why. He also tells Harper that up until the night of Homecoming, Mr. Hill had lived in a small guest house on his property before suddenly vanishing. David says he will go through the house to see if he can find anything.  

Later, Harper is invited to dinner at David's house by his aunt Saylor, who is in charge of the city's Cotillion Ball. While grasping Saylor's hand to say grace, Harper has a vision of girls in white dresses, ice, and people screaming. At the exact same time, David has a terrible headache and begins mumbling something about swans, power, and a new era rising. Saylor then reveals she knows that Harper is a paladin. She then launches into a bizarre story.

Saylor tells them she is not really David's aunt, and she technically kidnapped him as a baby after his parents were murdered. David is an oracle, and only one of two male oracles ever in history. The last male Oracle, Alaric, had very weak powers and his visions were not very clear, so he performed a ritual to increase them. This proved to work TOO well, and Alaric became incredibly powerful, and even granted powers to his paladins and the court mages. The power corrupted Alaric though, and kind Charlemagne had to lay waste to an entire city to get rid of him. After that a coalition (The Ephors) was formed to protect future Oracles from not only having too much power, but also being controlled by any king or government. Now, there is always one Oracle, a paladin and two mages, of which Saylor is one. Saylor and Mr. Hill were actually tasked by the previous Oracle to kill David, because the Ephors feared another male Oracle would be just as corruptible as Alaric. However, because of their oath to protect the oracle, they could not do it, and went into hiding with David while the Ephors searched them out. Saylor tells Harper this is now her destiny and they must work together to protect David. Both Harper and David protest, and tell Saylor that Harper can't be forced to be a paladin, and Harper pulls out of Cotillion, leaves and doesn't speak to David for several days.

However, eventually David speaks to Harper, telling her he has received an email asking him to go out of town to interview for a scholarship that he not only did not apply for, but also does not require an interview. Harper agrees to go with him to the interviews, both knowing it is likely to be a trap. Once they arrive they realize that, yes, it was definitely a trap, only the target was not David, the target is Harper. A woman named Blythe who turns out to be the other mage attacks her. Harper is able to subdue Blythe and tie her up, and Blythe tries to convince her and David that the Ephors are no longer looking to kill David. Blythe explains she is a much more powerful mage than Saylor (even though she is only 17) and she is sure she could do what Alaric could not, and make David both extra powerful and NOT crazy. They decide to take Blythe to see Saylor, but once they have Blythe in their car, she vanishes into thin air. 

Harper realizes she really has no choice but to be David's paladin, and try to figure out what is really going on in order to have the best chance of keeping them both safe. David tells her he is worried, because when he was a child he had a dream that Harper killed him. When speaking to Saylor they learn that in fact it was Alaric's paladins who killed him, as he had become a danger to himself, therefore creating a loophole for the paladins. 

Saylor begins to train Harper in combat, even though she is not really sure how to properly train a paladin. At one of the training sessions, David decides he wants to try to have a vision by using Harper as a conduit. He succeeds, but regrets the attempt, because the vision he has is of Harper dying at Cotillion. 

The night of cotillion, Harper's boyfriend breaks up with her, telling her he has known for a while she has feelings for David. Harper wants to tell him what is really going on, but obviously can't, so they end on friendly terms. Later, as they prep for the fight ahead, David kisses Harper telling her he just wanted to know what it was like (in case they both died). Harper realizes it's the best kiss of her life, but figures they can discuss it after the big fight. 

Before Cotillion even officially begins, Harper is attacked by Miss Annemarie, an 80-year old tea shop owner, who is clearly under some sort of spell. Harper realizes Blythe has put a mind control agent into the party punch, which basically everyone she has ever known has drunk. Harper manages to lock David in a room with the other debutantes, just before the entire town proceeds to attack Harper and Saylor, including her great aunts and Harper's best friend's boyfriend (who actually manages to stab Saylor). While trying to find Blythe among the attackers, it finally dawns on Harper there was one extra girl in the debs room - Blythe. 

By the time Harper fights her way back to the debs room, it is too late, Blythe has already started the ceremony to awaken David's powers. With a blast of energy, David, in an enchanted state, turns all the other debutantes into paladins. Blythe tries to escape with David, but David fights her mind control and instead, she vanishes with Harper's best friend Bee as a hostage. Saylor has sadly died from her stab wound, but not before passing her mage powers on to Harper's ex boyfriend. David uses his powers to de-paladin the other debs, (so that Blythe cannot hope to control them), and Ryan uses his new found mage energy to help wipe everyone's memories. 

The book ends with Harper, David and Ryan coming together to try and trigger a vision in David to see what is next for them.