This post contains lots of spoilers!!
Blue (yes, that is seriously the main character's name) lives with her psychic mom and her mom's two psychic friends in a small town in Virginia. Blue is not psychic but her proximity makes it easier for psychics. Every psychic she knows has predicted that her true love would die after she kisses him.
She goes with her aunt Neeve to a church on St. Mark's Eve, where her aunt will be able to see the people that will die that year. For the first time ever, Blue sees a spirit too. She asks his name and he tells her it's Gansey. Neeve says the only reason a non-psychic would see a spirit on St. Mark's Eve is if he's her true love or if she kills him.
Gansey is a rich kid who goes to a rich boarding school. He and his friends Adam (poor townie kid who's on a partial scholarship), Ronan (tough guy who has an attitude problem since his dad died), and Noah (who is pretty nondescript) are trying to find the ley lines so that they can wake some Celtic king who is supposedly buried along them. Gansey thinks a psychic might be able to help them find the ley lines so he makes an appointment with Maura, Blue's mom.
After the reading, Maura forbids Blue from seeing Gansey, which she of course defies. She decides she wants to help him find the ley lines. They find a strange forest where a tree shows them each a different glimpse of the future. They want to try a ritual to wake up the ley lines, but the ritual requires a sacrifice so they hold off. While walking the ley lines one night, Blue and Gansey find a dead body - it's Noah's. Apparently Noah has been dead for 7 years, but was able to manifest because of the ley lines. Once his body is moved, it becomes harder for him to manifest, but he is occasionally able to use Blue's energy to do so. They figure out that Mr. Whelk, their Latin teacher, is the one who killed Noah in his attempt to wake the ley lines 7 years ago. And he's going to try again.
Adam and Blue have a timid sort of flirtation. Although in the glimpse of the future she was shown, she was about to kiss Gansey. Gansey annoys her at first, but eventually grows on her. She is able to relate to Adam because they're both poor. Adam's father is abusive and Gansey continually tries to convince him to leave and come live with him, but Adam always refuses because of his pride. Eventually Adam's father beats him right after being dropped off by Ronan. Ronan sees and doubles back to attack his father. Ronan is nearly arrested, but Adam ends up pressing charges against his father and moves out.
Neeve captures Whelk so she can sacrifice him in the ritual. He's able to get free and tries to sacrifice her. Adam arrives to also try to ritual and stops them. He apparently sacrifices himself...except he still seems alive after the ritual... So I really don't know what happened there. So the ley line is awake and now the search for the Celtic king can really begin.