First off, let's make those generic highschool friends less generic. I seriously cannot remember any of them right now. Probably have one of them be prepared in case of EVERY POSSIBLE EVENTUALLITY. Jesus? Nailgun. Aliens? got the rifle right back here. Daleks? Here, have this thing with a blue light on the end. Jacob is the kinda sweet (and strong, and smart, and nice) dude she has a crush on but doesn't admit.
Vampires are changed to be only slightly better than humans under normal circumstances, aside from their one superpower. For my purposes it doesn't particularly matter if they can come out during the day or not, but at school the Cullen "family" is full of slackers.
This is a cover.
They get their food through hunting down people who are committing crimes and dealing with them, and OMNOMNOM in the middle of the act. This is how Bella first gets to know Edward; she is in a bookstore or something with a pal and OHSHIT ROBBERS WAIT WHAT WHO ARE THOSE PEOPLE WHY ARE THEY EATING THE ROBBERS OH GOD
So the next day at school is rather awkward. A strange relationship develops between the two, with Bella trying to unwrap the mystery of the Cullen family. Waking up to find a dude outside your window is played for scary stuff, even though Edward leaves quickly and doesn't come back to see her at night. This event prompts Bella learning how to deal with supernatural stuff, taking lessons from Dr. Helsing out in the woods.
In a side plot, her police father dad has to deal with an increasingly brutal string of murders. First some campers out in the woods, then Dr. Helsing, a family taking a roadtrip...the culprit displays a seemingly impossible level of strength and stamina, having ripped the doors off the car with ease.
Bella starts to suspect that the Cullen family did it, and some of the more brutal members of it suggest killing her. Edward vouches to protect her because he realizes that he'd like to be more of a hero and less of an antihero. Far away, a government agency takes note of these murders and considers investigating forks, in a plot that only really shows up in the sequel.
"prepared for everything" kid gets more paranoid, and eventually Bella's human pals decide to take levels in badass, led by the kinda jock dude she knows.
Bella, being the smart girl she is, decides to confront Edward out in the woods. Edward reveals to her that his family haven't been behind the murders, and as they both decide to team up and fight evil (with Edward taking remedial mercy classes). The meeting is then interrupted by a Vampire Bear.
You see, one of the Cullens is tired of the killing, and tried out fighting animals instead. It didn't completely work, and since the Bear's turning wasn't attended to, it became a Lesser Vampire-devoid of thought and reason, it lives only to find blood. Vampires such as the Cullens went through longer processes and are just better, with each one having a superpower. Greater vampires are the oldest and most powerful.
Edward's power turns out to be highly flammable blood, and he uses it to distract/wound the bear while Bella gets Helsing's Holy Elephant Rifle ready. After a good few shots between the eyes of the bear, it goes down and the two head back to forks, new crusaders for justice.
A massive black werewolf arrives on the scene just after the fight ends. It is (SHOCK) Jacob, and the book ends as Bella goes home and thinks on what her life will be like.
Plot points for future books-
Helsing's Legacy-all the things that badass mentor left behind, including a vial of Vampire Blood, potentially the earliest and most powerful sample ever obtained. Later turns out that dying was all part of his master plan.
The Forks Miltia-after such attacks, the normal people in forks start becoming badasses, eventually making for a small army of supernatural stuff hunters.
The MIB-They're the MIB!
Other Vampires-Not quite as nice as the Cullen family, and that's saying something.
Werewolves-Tradition holds that due to a magic ritual preformed at his birth, Jacob's destiny is to lead a wave of fur and fang, creating thousands of werewolves and returning america to a pre-columbian state. Trouble is he doesn't want to destroy american society as we know it.
Damn, that was a bit of writing there.