Arnie sees Christine one day as they are driving back from their summer jobs, and instantly falls in love with her, despite the appalling condition she is in. After a long argument with his parents, and despite Dennis' attempts to dissuade him, he buys the car from Roland LeBay, a war veteran who dies shortly later.
At LeBay's funeral, Dennis talks to his brother George, who reveals that the car has a gruesome history - Roland's daughter choked to death on a hamburger during an afternoon drive, and soon afterwards, his wife committed suicide in the car. Dennis is disturbed by both this and Arnie's obsession with the car - he is spending most of his time fixing her.
Meanwhile, Arnie's complexion, once awful, is clearing up at a remarkable rate, and soon Arnie's second love enters the scene - this time a girl called Leigh Cabot. She is the prettiest girl in the school, and soon she and Arnie start seeing each other. She too dislikes Christine, and often feels jealous of it and the time Arnie spends with it.
At about this stage, Dennis gets badly injured in a game of American football, and ends up in hospital until Christmas. He is therefore out of the action of the middle section of the book - although you'll see that he comes back for the ending. He is kept vaguely in touch with the situation though, and becomes quite worried for Arnie, realising that Christine is bad for him.
Throughout the book so far, there have been a few run-ins with another school-kid called Buddy Repperton. After the last one, a fight where Buddy draws a knife, Buddy is expelled, and Buddy and his mates decide to get their own back by smashing up Christine. They do indeed wreck it totally... and yet, only a couple of weeks later, Christine is roadworthy... looking better than before even. And then Christine starts killing...
While Arnie is still asleep one night, Christine rolls out of Darnell's garage and goes hunting. It is driven by the ghost of Roland LeBay, who plays a large part in the rest of the book, considering he's dead. Christine finds one of Buddy's friends, Moochie Welch, coming back from a concert where he's been spare-changing. He doesn't live very long, only long enough for Christine to have a bit of fun with him, playing a game with him. In the end though, Christine winds up rolling over his body again and again before returning to Darnell's.
Soon after, Rudy Junkins, a cop, stops by at Darnell's to talk to Arnie about the murder of Moochie Welch. Although Arnie has an alibi (his parents saw him sleeping at the right time), Junkins feels there is something strange about Arnie and especially about Christine.
One day, as Arnie and Leigh are coming back from a Christmas shopping trip, they stop to pick up a hitch-hiker before getting a burger. It is lucky for Leigh that they picked up the 'hiker, as she starts to choke on the burger, and it is only through his use of the Heimlich Manoeuvre that she survives. Of course, Arnie *knows* the Heimlich Manoeuvre, but didn't at the time - because inside there was more of Roland LeBay than Arnie Cunningham. Leigh takes an even stronger dislike to Christine, and resolves not to go in her again.
Christine continues her hunting, and this time it is Buddy Repperton and more of his friends that get killed. Again, Arnie has a cast-iron alibi, and Buddy sees that the car that is about to run him over has no driver. Junkers talks to Arnie again, and becomes even more interested in the car - as does Darnell. He slowly begins to make some connections, and becomes quite worried.
Soon, however, he has a lot more to be worried about - on one of Arnie's smuggling trips for Darnell, he is caught by the police and put in jail. His parents go frantic, and Darnell feels the net tightening around him - and his garage is closed by the police, pending investigation. Arnie, however, stays perfectly calm - or rather, LeBay does, inside Arnie's body.
After Christmas, Dennis comes out of hospital, and he and Leigh get closer - a little too close for his conscience. However, they start putting together the information they each have about what is happening to Arnie, and come to some disturbing conclusions. They decide they must set a trap for Christine and LeBay, and start going about it. They plan to entice LeBay with Leigh, who he lusts after. They know that Arnie will be out of town when the trap will be sprung, as he always is when anything happens with Christine. They find out that Dennis is planning to go on a trip to a university with his Mum very soon, and know that this is the time.
Around this time, Christine kills Darnell. No great loss. Similarly, Junkins crashes mysteriously, and dies. What causes the crash? I'll leave that to your imagination.
Dennis manages to hire Petunia, a huge lorry, and after calling Arnie's Dad to warn him to be careful and not approach Christine under any circumstances (LeBay is by now totally off his dead rocker) - and to ask him to give their own parents the same warnings - they go to Darnell's, unlock it with the copy of a key they borrowed on spurious grounds, and park Petunia inside. Unfortunately, Dennis slips over while they are unlocking the doors, and compounds his previously healing injuries so badly that he is unable to work the clutch with his left leg. He uses a broom to do it, but it's a major disadvantage.
Christine eventually arrives at Darnell's - with the dead body of Arnie's Dad in. It appears he didn't take Dennis' advice, and paid a mightily high price. Dennis is in the cab of Petunia when Christine arrives, but Leigh is outside, in the garage, and it is she that Christine first goes for. Leigh barely escapes, and Dennis starts Petunia up and rams Christine. She takes masses of damage, but keeps going - and starts regenerating herself. After a long battle, Dennis manages to knock Christine enough times for her to finally stop. Leigh runs to fetch help in the middle of the battle (it makes sense at the time, but is hard to explain quickly!) and they find Dennis in a terrible state, and unconscious. He gradually recovers, however, and eventually gets up the courage to talk to Junkins' partner and his own father about Christine. They both believe him as far as they are able, and things start becoming normal again.
Leigh and Dennis go out for a while, but don't end up happily ever after... in fact, the ever after is left open - all seems okay, and then, years later, the one surviving friend of Buddy Repperton is killed in a car accident. Dennis begins to wonder...