This sounds very much like the Stephen King story Nona.
It was published in the 1978 anthology Shadows and later collected in King's 1985 collection Skeleton Crew.
Nona is the story about a college dropout that hitchhikes in Maine a winter night. He encounters Nona at a bar and gets infatuated by her.
Someone tugged at my sleeve. I turned my head and
there she was—she’d moved over to the empty stool.
Looking at that face close up was almost blinding. I spilled
some more of my coffee.
“I’m sorry.” Her voice was low, almost atonal.
“My fault. I can’t feel what I’m doing yet.”
“I—” She stopped, seemingly at a loss. I suddenly realized
that she was scared. I felt my first reaction to her swim over
me again—to protect her and take care of her, make her
not afraid. “I need a ride,” she finished in a rush. “I didn’t
dare ask any of them.”
She made a barely perceptible
gesture toward the truckers in the booth.
How can I make you understand that I would have given
anything—anything—to be able to tell her, Sure, finish your
coffee, I’m parked right outside. It sounds crazy to say I felt
that way after half a dozen words out of her mouth, and the
same number out of mine, but I did. Looking at her was like
looking at the Mona Lisa or the Venus de Milo come to
breathing life. And there was another feeling. It was as if a
sudden, powerful light had been turned on in the confused
darkness of my mind. It would make it easier if I could say
she was a pickup and I was a fast man with the ladies,
quick with a funny line and lots of patter, but she wasn’t and
I wasn’t. All I knew was I didn’t have what she needed and it
tore me up.
“I’m thumbing,” I told her. “A cop kicked me off the
interstate and I only came here to get out of the cold. I’m
“Are you from the university?”
“I was. I quit before they could fire me.”
“Are you going home?”
“No home to go to. I was a state ward. I got to school on
a scholarship. I blew it. Now I don’t know where I’m going.”
My life story in five sentences. I guess it made me feel
She laughed—the sound made me run hot and cold.
“We’re cats out of the same bag, I guess.”
One of the truckers start to harass the dropout, but he goes berserk and nearly kills the trucker.
I straddled him, grabbed double handfuls of his greasy
hair, and began to rub his face into the gravel. In the flat
glare of the sodium light his blood seemed black, like
“Jesus, stop it!” somebody yelled.
Hands grabbed my shoulders and pulled me off. I saw
whirling faces and I struck at them.
The trucker was trying to creep away. His face was a
staring mask of blood from which his dazed eyes peered. I
began to kick him, dodging away from the others, grunting
with satisfaction each time I connected on him.
He was beyond fighting back. All he knew was to try to
get away. Each time I kicked him his eyes would squeeze
closed, like the eyes of a tortoise, and he would halt. Then
he would start to crawl again. He looked stupid. I decided I
was going to kill him. I was going to kick him to death. Then
I would kill the rest of them—all but Nona.
I kicked him again and he flopped over on his back and
looked up at me dazedly.
“Uncle,” he croaked. “I cry Uncle. Please. Please—”
I knelt down beside him, feeling the gravel bite into my
knees through my thin jeans.
“Here you are, handsome,” I whispered. “Here’s your
I hooked my hands onto his throat.
Three of them jumped me all at once and knocked me off
him. I got up, still grinning, and started toward them. They
backed away, three big men, all of them scared green.
And it clicked off.
Just like that it clicked off and it was just me, standing in
the parking lot of Joe’s Good Eats, breathing hard and
feeling sick and horrified.
They escape the bar together and manage to get a lift with a man called Norman Blanchette. The dropout get annoyed with Norman for seemingly no reason and Nona encourage him to kill Norman by providing him with a nail file.
I got out. Nona slid across the seat, giving Norman Blanchette a final smile. I wasn’t worried. She was
quarterbacking the play.
Blanchette was smiling an infuriating porky smile,
relieved at being rid of us.
“Well, good ni—”
“Oh my purse! Don’t drive off with my purse!”
“I’ll get it,” I told her.
I leaned back into the car. Blanchette
saw what I had in my hand, and the porky smile on his face
Now lights showed on the hill, but it was too late to stop.
Nothing could have stopped me. I picked up Nona’s purse
with my left hand. With my right I plunged the steel nail file
into Blanchette’s throat. He bleated once.
They continue hitchhiking and kill most people they encounter, including the police. In the end they reach the destination Nona claim she was heading to, which turns out to be a graveyard. Nona leads him to one of the tombs and inside he find Nona's dead body, mutilated and full of rats. The dropout and Nona embrace and she transform into a rat-creature.
I went to Nona. I went to my life.
Her arms reached around my neck and I pulled her
against me. That was when she began to change, to ripple
and run like wax. The great dark eyes became small and
beady. The hair coarsened, went brown. The nose
shortened, the nostrils dilated. Her body lumped and
hunched against me.
I was being embraced by a rat.
“Do you love?” it squealed. “Do you love, do you love?”
Her lipless mouth stretched upward for mine.
I didn’t scream. There were no screams left. I doubt if I
will ever scream again.