This book begins with a description of how love has been decided on as a disease, and at everyone's 18th birthday they are forced to undergo a procedure to cure them of the "deliria". Lena is almost at her 18th birthday and cannot wait to undergo the procedure to prevent the contagion of deliria, since she saw what it did to her sister and mother. Lena has always been told that her mother killed herself when Lena was 6 by jumping off a cliff near their home due to her strong feelings for Lena's father who passed away. Her mother underwent 3 different procedures to cure the deliria but they never took hold. We later find out that Lena's mother is still alive and has been kept imprisoned in the Crypts ( a type of jail/asylum where they keep everyone who is seen as a "sympathizer" to those with deliria or who have it themselves).
Lena meets a boy by the name of Alex, and begins talking with him because she thinks he is cured. She begins falling in love with him, though she doesn't really realize that's what's happening, and he eventually tells her that he was never cured, and the scars on his neck that represent the procedure were inflicted by the Invalids (ppl who live outside protected cities) so he could come live in the city out of the Wilds. Lena is angry at him for lying to her and tells him to leave her alone.
Hana is Lena's best friend who talks Lena into going to a party where Uncured people will be. There is unapproved music at the party but Lena loves the sound although she won't admit it. Later Hana tells Lena that she is going to another party but Lena is scared to go and stays home. There is a raid that night so Lena runs off to warn Hana so she won't get caught and Lena herself is injured at the party by the regulator's, but Alex comes to her rescue and from that point on Lena is hopelessly in love with Alex.
Lena tells Hana about Alex after Hana discovers him sneaking it to see Lena at her work and Hana becomes an ally to help Lena see Alex from then on. They find an abandoned house on the outskirts of town and it becomes their meeting place.
Lena is matched with another boy after her test, and the boy comes by to see her and tells her that he was in love with another at one point in time too but that things will be better and she will forget Alex after the procedure. Alex is standing nearby and hears this. He walks away, thinking Lena has chosen to have the procedure after all, but Lena goes after him and finally declares her love. This is the point where Lena describes something her mother had and Alex tells her he thinks she is still alive, although when they go into the Crypts they discover her mother recently escaped. At the abandoned house she is captured and taken hostage in her home. She finds out they have planned to move the procedure up by a week, and although she had planned to run to the Wilds with Alex, she now can't get word to him that it's planned for sooner than expected so she sends Hana with a message to put in the fist of The Governor (the statue she used to run by in her marathon's with Hana) in hopes that Alex will find it and rescue her.
He does come to rescue her, and Lena takes off with him on a motorcycle with regulators in pursuit. The fence Alex and Lena used to go into the Wilds where Lena could see it wasn't bad a couple weeks prior has now been electrified, so Alex tells her to jump at the last second and they are going to ram the bike into the fence to short circuit it. It works and Alex tells Lena to climb the fence and run, but when she looks behind her he isn't following and she sees that he has blood all over him and has been shot. The last thing she sees is Alex mouthing the word run and the regulators swarming over him. END OF BOOK 1