LEWISTON – Best-selling author Tess Gerritsen figures she’s a little twisted.

When her teenage son asked her for haunted house ideas, she jettisoned the usual white sheets, creaky floorboards and organ music. Instead, the ex-physician imagined a gory hospital scene.

“We could go to the butcher and get some entrails,” she suggested. It grossed him out.

“My kids like scary movies but they’re not like me,” she said Thursday, with a hint of a smile. As a girl in San Diego, where she grew up, Gerritsen picked up her mother’s love of horror.

“I spent most of my childhood screaming in the movies,” she told attendees of the Great Falls Forum at the Lewiston Public Library. “I always try to reproduce that feeling of a 5-year-old in a dark theater.”

It’s been a good strategy.

Gerritsen’s last 11 novels have been best-sellers, including her latest, “The Bone Garden.”

The medical thriller is set primarily in 1830 Boston as a group of “resurrectionists” harvest cadavers for sale on the black market.

It’s the kind of topic that draws some puzzled questions from readers of the woman who settled with her family in all-too-quaint Camden.

One of the recurring questions is why write such stories?

“A woman will say, ‘They’re so gruesome and gory and scary. Are you sick?’ ” Gerritsen said.

She didn’t start out writing medical thrillers. Her first books were romances, a nod to the escapist literature she’d read as a student.

Her publisher didn’t even know she was a doctor until she announced that she wanted to write a story about street children being kidnapped and killed for their organs.

“I didn’t think medicine was all that interesting,” she said.

It became her first best-seller.

The idea had grown from a conversation with a friend who’d recently visited Moscow and told a chilling story of missing kids. It stuck with her.

“The best ideas are like a whomp in the chest,” she said. She gets shocked, sad or angry, she said.

The stories grow from there, mixing with her sensibility. They might take off with an examination of blood – what she calls “a biochemical soup” – or old stories about 19th century women dying from something labeled “childbed fever.”

Her research into stories from the era found that huge numbers of women were dying in the hours and days after childbirth.

The reason: poor hygiene.

“The doctor’s were killing them,” Gerritsen said. When they eventually started washing their hands, the cases of blood poisoning disappeared.

The episode led her to study medical schools of the era and the market in cadavers, which grew from the need of medical schools to have bodies to examine.

The barbaric medicine and the grave-robbing become part of “The Bone Garden,” which went on sale last fall and quickly hit The New York Times best-seller list.

The idea – that a market in dead bodies lead to lots of grave snatching – also drew a sinister smile from Gerritsen Thursday.

She mused that anyone who tried to dig up New England’s old cemeteries might be surprised by the missing bodies beneath the tombstones.

“There would be empty coffins everywhere,” she said.