Sunny is convinced by her identical twin sister, Rayne, to go to Club Fang (dance club for goths) in a T-shirt borrowed from a vampire that says “Bite Me.” Rayne guarantees that her sister’s virtue will stay in tact as most goth guys are gay.
Rayne goes to get drinks. Sunny is waiting for her when she is approached by Magnus. She thinks he is hot and lets him drag her outside to talk. He asks if she is sure she wants “this” and she confirms, thinking he means kissing her. Magnus does kiss her and then moves down her neck and bites her.
Sunny demands to know why Magnus bit her and he pulls out a contract that Rayne signed. Sunny explains it is her sister’s signature. Rayne comes out and tells Sunny she has accidentally started the transition to becoming a vampire.
Sunny doesn’t believe that Magnus is a vampire until he stabs him in the stomach, thinking the knife is a trick blade. She freaks out when she realizes it is real. Magnus pulls it out of his stomach and heals. He explains that he has fang implants that contain his blood. She is infected. They will have to talk to Lucifent (his 3 thousand year old boss) to see if this can be reversed before the 7 day transformation is complete.
Unable to sleep, Sunny goes to talk to Rayne, who is obviously upset that Sunny was bit instead of her. Magnus was supposed to be Rayne’s blood-mate (a vampire can only run one person per their laws, and they should have a connection). Rayne will have to start the process over. she gives sunny material to read from her transformation classes.
The next day at school is a blur to Sunny since she didn’t get much sleep. When she gets to play practice, she is told she will be filling in for the lead of Bye, Bye Birdie. She gets to rehearse the kissing scene with her crush, Jake, and afterwards, he asks her to prom. Rayne comes along to tell her about her new pheromones and scold Sunny for not reading her blog. Mr. Teifert overhears them laughing over vampire jokes and asks if Sunny really is one. Sunny lies and Rayne is suspicious.
Rayne takes Sunny to the cemetery to meet Magnus, who says that Sunny will have to go to the Coven with him alone. He takes her to the under mansion through a dark tunnel and she has to keep reminding herself that she shouldn’t be attracted to Magnus. She gawks at the wealth around her before Magnus pushes her on.
They walk to Lucifents office and Marcia lets them in. Sunny immediately sees a little child and starts treating him like one. When it is evident that the child-like vampire is Lucifent, she laughs at him. Magnus explains the situation and says he is willing to pay the price for his mistake. Lucifent tell her that there is a way to reverse it.
As Lucifent is about to help Sunny, alarms start going off. Bertha the Vampire Slayer has entered the compound. Lucifent, Magnus, and Sunny start heading for safety, but Bertha comes out of no where and stakes Lucifent. Magnus and Sunny escape to a room with a secret passage behind a bookshelf.
Locked in a safe room surrounded by titanium, Magnus and Sunny are forced to wait out the Slayer incident. Magnus gives her a little history about how the slayers won’t back off even though the vampires are no longer a threat. He explains that Lucifent turned him in the crusades when he found him dying in a prison and has been waiting to be approved for a blood-mate ever since.
Once they are given the okay, Magnus takes Sunny home where she finds Rayne asleep in her bed. She asks her twin to stay with her through the night. The next morning at breakfast, Sunny learns that the smell of garlic makes her sick. She puts on sunscreen and returns to the kitchen. Without thinking about it, she starts eating raw ground beef even though she is a vegetarian. She vows to never drink blood.
At school, Sunny has teachers flirting with her before being called down to the principal’s office. When she gets there, roses from Magnus are waiting for her to apologize for the whole situation. There is a note asking her to meet him at club Fang to discuss it.
Sunny meets Magnus at Club Fang, which now looks like a trendy coffee shop. He has his blood donors, Rachel and Charity, with him and they give her a glass of blood, which they tell her is wine. Magnus tells her the transformation can be reversed with a drop of blood from the holy grail.
Magnus explains the history of the grail to Sunny and she feels like there is no hope. He offers to take her to England to see if it is where it has been rumored to be. Jareth, head of the vampire army, interrupts them to tell Magnus that other vampires will try to take his thrown (he is Lucifent’s successor) while he is away. Sunny asks if Magnus really has time to help her, but he is determined to fix his mistake. They break away from their blood-bonded sexual tension with plans to meet the next day.
Sunny’s mom is waiting for her when she gets home. She thinks that Sunny is on drugs from the way she is acting. Since she won’t admit it, or tell her mom what is really going on, her mom grounds her.
Sunny goes to Rayne for help. Her twin suggests that the switch identifies for the day so Sunny can get to England. Rayne explains that Magnus was determined to be perfect match through DNA testing (and since they are identical twins, they have identical DNA).
While on her way to switch clothes with Rayne, Sunny is approached by Jake. He says he wants her and starts making out with her, but she’s not into it because she knows it is not real. She thinks he will forget about her when she is human again and leaves to meet Rayne.
On the fancy private vampire jet, Sunny gets comfortable and falls asleep. When Magnus appears and wakes her up, they are in England. They will stay with another coven during the daylight and then travel an hour by car to find the grail. Magnus asks how she’s really doing and she is honest with him.
They come to the above ground headquarters of an England coven and they offer them a room to stay in. Sunny asks why they won’t be in separate rooms and Magnus explains that it would be a bad move politically for him. they share a giant bed and keep to separate sides.
Night falls and they take off to find the grail. However, there is a music festival going on in the town that sends the guardian druids into hiding. Sunny finally breaks down crying, loosing all hope. Magnus says that he will stay with her as long as she wants if they aren’t successful and kisses her.
They decide to attend the festival and end up dancing the night away. Sunny tires to keep the situation platonic but isn’t sure she can.
The next night, Sunny and Magnus wake up and he wants to talk. he asks to put it off and they go to find the druids now that the tourists have left town. He agrees and when they arrive, Magnus offers the Pendragon 1 million pounds for him to take them to the grail. Sunny overhears the Pendragon talk it over with a friend. He eventually lets his greed get the better of him and takes them to the cup. Magnus starts sweating blood as they get closer. They are given two vials of blood and she must take one on Saturday.
Back in the US, Magnus takes Sunny home. He offers to stay with her through the transformation back to human. she turns him down, explaining that she has a date. She wants a clean break so she doesn’t tell him how she feels about him. He drives off and she cries.
Rayne finds Sunny crying blood and asks what happened. Sunny tells her they get the blood, but she loves Magnus. Rayne tries to tell her the perks of becoming a vampire, but Sunny thinks it is so Rayne can be moved up on the waiting list. Sunny explodes on her twin. Rayne storms off saying she is going to take Magnus.
Sunny notices the difference in her appearance since the transition. She gets ready for prom and Rayne comes by to make sure that Sunny really wants to be human again. She lies to Rayne and to herself.
At the prom, Sunny is bored and missing Magnus until Rayne shows up with him. She leaves Sunny and him alone, but the moment is destroyed when Jake starts kissing her. Magnus storms off and Sunny runs after him. She says she wants to be with him and smashes her vial of blood. Magnus leaves her for a moment while she freaks out about loosing her humanity. He kisses her and then bites her neck.
Magnus put the grail blood in he teeth implants. Sunny can’t decide if she is happy to be human or sad to loose Magnus. He tells her he wants to be with her no matter what. They kiss.
The Monday after prom, Rayne is pulled aside by Sunny’s drama teacher. He tells her Bertha is temporarily retired and that she, Rayne, is the next slayer.