NEW YORK -- Kate Morgenroth insists she has a sinister side. Still, the freckled-faced 27-year-old seems more likely to break into a medley of show tunes than embark on a murder spree.

At the moment, that gruesome alter-ego must be hidden behind her charming chipmunk voice, blindingly sunny smile and cartoonish expressions. But it surfaced plain and clear in her debut novel, "Kill Me First."

Heavy on dialogue, skeletal in description, the psychological thriller features a mass murder in a retirement home, among other random grisly acts. "When she pulled the trigger, she wasn't ready for the recoil," Morgenroth writes. "The pistol jerked, and the bullet went through the man's nose. Right before her eyes, his nose disappeared into fragments of cartilage and blood."

The author knows her gory tale must have shocked her editor.

"Here was this meek, nice, little thing, and I was giving him a book with mass murder," she says.

Released this spring, the shocking page-turner has garnered enthusiastic reviews and is already in its second printing. Kirkus Reviews called it "a white hot debut," and Publisher's Weekly described it as "a clever and unusual thriller, unflinching in its violence."

Fellow writer Erika Holzer praises Morgenroth's sophistication. "The psychological suspense and maturity she shows was stunning to me," says Holzer, author of the thriller, "Eye for an Eye." "A lot of writing courses say, 'Write what you know.' I don't buy that one bit. It takes courage not to write about yourself. It also takes more imagination, frankly."

Seated at a metallic table in a funky Greenwich Village cafe, Morgenroth eagerly slices a fat cinnamon roll into even sections. The Princeton grad, who seems like she's been intravenously supplied with Jolt Cola for the past 24 hours, covers everything from her love of the New York Knicks to her appearance at Bibelot in Canton tonight at 7.

She's written a novel that, contrary to those of most young authors, is not thinly veiled autobiographical fiction. Morgenroth wasn't out to prove anything by veering from her own experience. She already knows her own story. She'd rather tell another one.

"I'm not confident that I'm so amazingly interesting, that people are going to want to sit and listen to what I have to say if I wrote a book with me as the main character," she says. "I think I'm intimidated by things I know too well. It's much easier for me to create it on the page, instead of try to replicate it on the page."

But she never intended to write a thriller. It just came out that way. The excessive, exotic characters and situations in her book are not part of her Westchester County, N.Y., upbringing or anything following. But her seminal idea for the novel is one everyone can grasp, even if they haven't been held hostage during a mid-life crisis.

"At a certain point in life, you think things are set, and you think that's the way things are going to be," Morgenroth says. "But really, there's just as much chance it could change drastically. Random chance could knock you out of your orbit."

This notion is personified by Morgenroth's Sarah Shepherd, a middle-aged woman who goes from a hyper-predictable married life to something considerably more dangerous.

To complete the book, Morgenroth quit her job in HarperCollins' marketing department. She'd prepared for this bout of unemployment by saving enough cash to live on for roughly half a year.

She knew the concentration it would take to write a novel. She'd already written one at Princeton, where she was an English major with a creative writing concentration. Morgenroth has no intention of ever trying to publish "Detour," a grim story of a young female hitchhiker. She wrote it as her senior thesis, under the direction of her professor, Toni Morrison.

With no book contract and no guarantee of returning to her job after she finished, Morgenroth retreated into a monastic lifestyle.

"I was basically writing against the bank account," she says. "I didn't spend anything. I really didn't go out at all."

Her "amazing cheapness" also led her to The Strand, a huge discount New York bookstore. In starving student style, she sold back books for money.

Morgenroth mostly sold nonfiction, and she regrets selling back a biography of Mozart. She would never dare sacrifice her favorites, Trollope and Austen, whom she describes as literary "comfort food."

The Strand clerks may have thought she was a struggling undergrad. Even at 27, she looks like one in a V-neck T-shirt, airy black pants, black flip-flops and the telltale backpack.

After she finished the first draft, Morgenroth returned to HarperCollins as a temp, editing her own book in her spare time. When she got it somewhat polished, she brought it to HarperCollins executive editor Larry Ashmead. She knew him informally, and hoped he would give her advice, or a referral to an agent.

"I really did groan when she came in," says Ashmead, who has had many a young colleague hand him a stack of unpublishable ambition. "I agreed to do it because she's such a good person and so charming. She always has brownies, cookies or something for the department."

Morgenroth knew the idea of the aspiring writer, traipsing into an editor's office, first novel in hand, was a cliche. And she could sense how an editor would respond. "What do you expect? Do you expect me to buy this book?" she said, acting the role of exasperated editor. "Not!"

Not quite. Just a couple of weeks after she handed it off to Ashmead, he asked her to come up to his office and discuss it. He liked it, and wanted to show it to a few people.

"I didn't know he has a very dark side," Morgenroth says. "Little did I know I was giving it to the perfect person."

Soon after Ashmead met with her, Morgenroth, who didn't even have an agent, was offered a two-book deal. Now she is working on her next book, and living off her advance. If you can call it living.

"I'm still trying to figure out how to write and have a life at the same time," she says. "I can't seem to do it. Either I'm living or I'm writing."

She'll only give a couple of hints about her next book.

It won't be about her. And it's likely to be an outlet for her dark side once again. It's more a cynical attitude and appreciation of irony than over-the-top hostility, she explains.

"I'm not that scary," she says.

Kate Morgenroth

Appearing at Bibelot, 2400 Boston St., in Canton tonight at 7. Information: 410-276-9700. Pub Date: 6/29/99