Early one morning, Bethany descends to Earth with her companion angels, Ivy and Gabriel, arriving in the small town of Venus Cove. The three have been sent to help stem the tide of the bad things happening in town. As the youngest, most inexperienced and most human of the angels, Bethany enrolls in the local high school to blend in with the other teenagers, her brother angel, Gabriel, becomes the music teacher there, and her sister angel, Ivy, starts volunteering in town to make changes that better the community.
Bethany finds high school overwhelming because her angel senses are attuned to all the new physical sensations around her. She meets Molly, who helps her navigate the hallways and social traps of high school. Bethany tells her that Gabriel and Ivy are her siblings and that they are waiting for their parents to return from overseas. On her first day of school, Bethany also meets Xavier Woods. She immediately falls for this charismatic young man, even though attachments to their human charges are forbidden. Gabriel and Ivy warn Bethany to be careful, both in her friendship with Molly and her attraction to Xavier, but Bethany allows her new emotions to lead her astray. Molly also warns Bethany about Xavier. Ever since his girlfriend was killed in a tragic house fire, he hasn't had a relationship with anyone.
Molly asks Bethany to her house for a makeover party. After pleading with Gabriel to let her attend, Bethany is shocked to discover the makeover emphasis has been replaced with drinking alcohol. The young angel knows she should leave immediately, but she is curious to see what her classmates are doing. She accepts someone's offer of a drink; in fact, she has several, not realizing they have alcohol in them. When she begins to pass out, Xavier finds her and takes her home. Bethany fears her fellow angels' rebuke, but Gabriel and Ivy take care of the physical ramifications of her evening without punishing her. They understand that in her human form she's bound to make some mistakes. They spend a quiet day together, although Bethany is angered when she reads an article about violence in the Middle East and is told by Gabriel that they cannot intervene. Their jurisdiction is Venus Cove. They must let others take care of the rest of the world. Later, at a store, Bethany decides to help an elderly woman who must put her dog up for adoption. Bethany agrees to take care of the dog and bring it to the nursing home to visit the woman. Gabriel and Ivy welcome their new pet.
Xavier asks Bethany out on a date. Her fellow angels caution her not to accept. Although upset at first at their intrusion, Bethany realizes they are probably correct. She tries to ignore her feelings and plans on standing Xavier up, but on the night in question, she sneaks out of the house and meets him at the movie theater so she can tell him in person. He convinces her to have coffee with him. The two have a wonderful time talking, although Bethany can share few facts about her life. Gabriel is angry when Bethany returns home, but she cannot see what harm can come from her relationship with Xavier. At school, he becomes overt in his feelings for Bethany, sitting with her at lunch and asking to spend more time with her.
One day, the two come across a car accident outside the school. Bethany and two other students drag the driver from her car, unconscious. Before the driver can die, Bethany wills her to breathe and stay on Earth. Gabriel arrives and helps to heal the girl's internal wounds. Bethany passes out from the exertion, surprised later to learn that she had used her own life force to save the girl's life.
Bethany's feelings for Xavier continue to grow. At a bonfire she gets Xavier alone and tells him the truth of her identity, going so far as to unfurl her hidden wings and show him how she can fly. She is afraid that once he learns the truth, he will leave her, but he accepts her for whom she is and promises to keep her and the other angels' secret. Gabriel is furious with her betrayal and leaves to speak with the other archangels to determine what should be done. Gabriel returns, aggravated that a higher authority has overruled the covenant and that Bethany will be allowed to stay on Earth. She is delighted until Gabriel invites Xavier over for dinner. She fears her brother angel will make things uncomfortable for her new boyfriend. Xavier makes a good impression on the other angels and promises to help protect Bethany.
A new student, Jake, arrives. His English accent and bad-boy attitude quickly make him popular with the students. He and Bethany become partners in their English class and must write a love poem together. Jake's flirtations make her uncomfortable, but she tries to remember he is new to the area and makes friends with him. She overhears him trying to seduce the English teacher, who, although clearly attracted to him, tries to halt his advances.
Things begin to change around the high school. Bethany puts it down to Ivy's charitable work. There seems to be a new camaraderie among the students, although their primary concern is still the upcoming prom. Molly is bewildered that Bethany and Xavier haven't had sex yet. Her disbelief causes Bethany concern as she wonders whether Xavier is hiding his desires from her. Molly visits Bethany's house and tries to get Bethany to help her win Gabriel's affection. Bethany warns her that Gabriel is not like ordinary men, but Molly refuses to be swayed. She even starts volunteering with them in the community.
Xavier breaks his ankle and gets a concussion at a rugby game. Although he will heal, he is unable to take Bethany to the prom. At first, she wants to stay home, but Xavier insists she attend. Ivy has made a dress for her, and all her friends will be there. Jake asks if he might escort Bethany, and she agrees after talking it over with Xavier. She is wary when both Ivy and Gabriel have a negative reaction to Jake, but she ignores the warnings, as she knows both her angel siblings will be at the prom if she needs their help.
Bethany and Jake are named prom king and queen. After a mandatory waltz, Jake finds a way to escape the venue and get some fresh air. They argue when Jake insists that Bethany should break up with Xavier and date him. Jake stops her from leaving and kisses her. When Bethany refuses him, Jake threatens her. She begs Gabriel and Ivy to take her home. Bethany spends the rest of the weekend stressing about Jake's actions. She begins to worry when she doesn't hear from Xavier that something has happened to him. The following day, Molly shows her a picture of Jake and Bethany kissing that has been posted on Facebook. Bethany leaves school and heads to Xavier's house. He has seen the picture. He refuses to listen to her excuses, convinced that she cheated on him with Jake. That night she dreams that Jake pushes Xavier off a cliff. She becomes despondent over the breakup, refusing to eat or leave her bed. After several days, Gabriel and Ivy ask Xavier to come visit her. When he sees the state she's in, Xavier forgives her. They express their undying love for each other.
The angels and Xavier suspect that Jake is more than just a troublemaker. Several accidents have occurred in and around the school since his arrival, especially since the prom. When one of Bethany's friends kills herself in the school bathroom, Bethany sees Jake talking to the police. He flashes her a satisfied look before leaving the scene. Bethany has a vision, in which she sees her friend struggling not to kill herself, but unable to resist some unseen force compelling her to take her life. Later, Jake sends a poem threatening Xavier's life.
Molly is excited when Jake asks her out on a date, but when Bethany cautions her against him, Molly turns on her. Bethany fears Jake will hurt Molly, but Xavier insists Jake won't do anything while he is recruiting students into his inner circle of friends.
Gabriel and Ivy warn Bethany to wait until they've consulted with a higher authority before going after Jake and Molly, but she decides against it. After they figure out that Jake has taken Molly to the local cemetery, Xavier and Bethany go after him. They find him holding a ceremony among the graves in which he calls on demons to possess the bodies of the "friends" he's brought with him. After they watch one boy being possessed, they are shocked to see Molly brought into the circle of followers next. When they try to stop the ceremony, Jake attacks Xavier. First Jake tells him that he killed his first girlfriend, and then he attacks Xavier physically. Bethany rushes forward, offering her life for Xavier's and Molly's. Jake drains her of her powers, drugs her, and then transports her to his home. There he tortures her with images of violence and hatred, threatening to blacken her soul so badly that she will not be allowed back into heaven.
Gabriel, Ivy and Xavier arrive to save Bethany. She is almost dead, but Xavier's voice begs her to hang on. Gabriel and Jake battle, but Gabriel's sword of light seems unable to fatally wound the demon. Bethany sees that there is a bright light surrounding her and Xavier. Ivy tells her to use her gift, and Bethany understands it has something to do with the light. She and Xavier kiss, and Jake is thrown back by the light exploding from the couple. He is wrapped up by tentacles of darkness and dragged into a black abyss. When Xavier asks what happened, Ivy explains that it was their love that drove the demon away.
The demons that possessed the other students are driven away, and Ivy helps the students forget what happened to them. Bethany has trouble recovering from the ordeal, still remembering all the horrible images Jake forced her to see. After three months, everyone seems to be recovering well — until Bethany discovers a threatening note in her locker from Jake.