There's one novel, Cujo, that I barely remember writing at all. I don't say that with pride or shame, only with a vague sense of sorrow and loss. I like that book. I wish I could remember enjoying the good parts as I put them down on the page.

– Stephen King, On Writing

Stephen King knew he was an addict in 1975, when he was writing The Shining. It manifested in his writing, as part of what he was doing; hidden from everybody else, it was in him, and on the page. Back then, it was only alcohol. As he became more popular, wrote more, earned more, took more time away from his family to work, his addictions escalated. How could they not? He needed to hit deadlines, and he liked the taste of what he was addicted to. You can see it through his fiction: in Jack Torrance's alcoholic self-pity, desperately scared of becoming what he's destined to be, trying to hold his family together even as he shakes it apart; in Larry Underwood throwing his life (and money, and 15 minutes of fame) away on drink and drugs at the start of The Stand; in his short stories, tales of addiction and internal collapse and death. Then, in case all this passed you by, along comes Cujo: and in the giant, slobbering, seemingly unstoppable dog, we find the bluntest metaphor for addiction yet presented in King's oeuvre (a title it would hold until Misery and The Tommyknockers).

No ghosts, only the vaguest hint of any supernatural aspects (see the Connections section below), no secret government institutes: Cujo is simply a lovable St Bernard. Until he isn't. His owners, the Camber family, are distracted by the day-to-day hassles of their lives; and by Joe, the patriarch, being a bad father/husband (in the grand King tradition of those). Because of this, they don't get poor Cujo – a dog that Joe is disinterested in at the best of times – vaccinated against rabies. When the dog goes poking his nose into caves, he gets bitten by a bat – a nod to Salem's Lot there that can't be ignored – and becomes rabid. And so the book's bad guy is born: a beast whose actions are beyond his control, who kills those inhabitants of Castle Rock who cross his path, one by one. A lack of control leading to evil: another of King's dominant themes in these early novels.

In fact, though, Cujo spends most of the book involved with Donna and Tad Trenton. Recently moved to Castle Rock, the Trentons are nice, responsible people, the sort who definitely wouldn't have forgotten to get their dog inoculated. They're the sort of people who shouldn't be destroyed by forces beyond their control. But when their own family patriarch, Vic, is away, Donna and Tad are locked in the family car (and for a large portion of the book) while Cujo terrorises them. For them, characters who are conventionally set up to be the survivors, the book ends not with a bang but a whimper: Donna, having been bitten by Cujo, eventually drives a broken baseball bat through the dog's eye. Tad isn't so lucky: he dies in the car. Not because of Cujo, or not directly; but due to dehydration.

As I say, it's all one giant metaphor for King's addiction. Metaphor is there in all fiction if you look for it, of course, but this book aches with symbolism. On the outside, Cujo is cuddly, pleasant, likable. When he's bitten – and maybe that bite from a bat can be directly equated to King's Salem's Lot success – he changes. Filled with uncontrollable rage, foaming at the mouth, unable to be the good dog he was. As King writes: "He had always tried to be a good dog. He had been struck by something … free will was not a factor." He – Cujo, King – is trapped inside whatever's driving his body for him. He hurts those he loves. He is brutal and remorseless, because he is not himself. Those who would stop him are cut down or trapped. They can only look at him through windows and pray he leaves them alone, or that they get a chance to stop him. Even when the demon is dead, it still kills them. Well, no. Actually, what kills Tad is his desperate need for a drink.

Maybe that's too much. Maybe we have to come at this from a Barthesian position, standing back: this is a scary book about a rabid dog. But I simply don't believe we can. King cannot remember writing the book, but he did. Daily, he sat at his keyboard and drank himself into a stupor and beat the keys, and at the other end Cujo was sent to his editor. Somewhere inside, his subconscious was driving: something had to be.

Many of his books from this point on are less than subtle with their metaphor. That isn't a criticism: I think King does some of his best work when looking inward, consciously or not. It's not always pretty, but it's always interesting. It's not as if Cujo was the first of his novels to mine the alcoholism metaphor – The Shining told the story of an ex-English teacher with a drinking problem – but this is the point at which it became the book. Not a character, but the whole text.

Structurally, Cujo is fascinating. There are no chapters, no page breaks: it's a constant rush of words, darting between characters and with reminiscing periods of backstory, but always pushing forward. Like the plot and the dog – and, yes, King's addiction – it's unrelenting. The book stops when the dog does, or just after, as the families try to pick up the pieces of their lives in the wake of the chaos that has wrecked them. The surviving members of the Camber family, Cujo's owners, buy a new dog. This one is vaccinated, but here's the thing: it's still a dog. The potential for what it could do, how it could turn on you, is always inside it.

Reading interviews with King from the time when his addictions weren't public knowledge, he feigns normality, pretends he knew what he was doing when he wrote Cujo. Now, after he's admitted that he was then suffering his worst bout of alcoholic torpor, we know it was all a lie. Cujo is as much a surprise to him as it is to the reader: the brutality, the pace, the agony inside. It's a tremendous book – more tremendous, in my view, when you know how it was written, and how absent King really was. It's scary, it's tense, it's incredibly pacy. And it's another non-supernatural book. It's a shame King can't remember writing it, that he can't revel in his creation of something this good. But what's not a shame is that we have it: not only as readers of great fiction, but as admirers of a man who was suffering and couldn't face his demons in person, so put them directly on to the page.

Connections

Cujo – either the dog itself or the deaths it rendered – is invoked in several other Castle Rock novels: The Tommyknockers, The Dark Half, Needful Things (all books, incidentally, that deal with King's addictions in their own ways). There's a bigger connection, though: to The Dead Zone, in which Sheriff George Bannerman asks for John Smith's help to catch the Castle Rock Strangler, Frank Dodd. Bannerman reappears in Cujo and meets his end at the dog's teeth. But another character also makes the transition to this book: Dodd himself. It's weird, and vague, but we're told at the start of Cujo – on page one – about Dodd, and that "the monster never dies … It came to Castle Rock again in the summer of 1980", when Cujo is set. It's suggested, briefly, that Dodd is somehow the darkness haunting Tad Trenton's closet; that he's a part of the darkness that fills Cujo and drives him to commit his horrible killings. This is another common theme of King's: the sense that evil is innate, and more powerful than the individual instance. It's never made totally explicit in Cujo, but it's definitely suggested: Cujo, Frank Dodd, the other darkness that will, in later books, invade Castle Rock – they're one and the same.

Next time

We're raining fire, flying planes and somehow being played by Arnie in the film of the same name: it's The Running Man.