WILTON — At least one half of the sister-writing duo Lynne and Valerie Constantine never thought she’d wind up as a thriller writer, but here they are with their third book — “The Wife Stalker” — which takes a familiar plot of two women vying over one man and turns it on its head.

The sisters write under the pen name Liv Constantine, and they will join Wilton Library in a videoconferenced author talk on Tuesday, June 23, at 7 p.m. Registration is required through www.wiltonlibrary.org.

The women began their collaboration about 20 years ago when they wrote a more conventional novel based on their Greek family. For 10 years that was it as the two, 13 years apart, moved on with their lives and different careers. Valerie worked early on in the White House planning presidential trips and Lynne worked in marketing. Lynne moved from home base in Maryland, where Valerie still lives, to Connecticut, raising and homeschooling twins. But she never lost the writing bug.

A fan of the thriller genre, Lynne soloed, writing “The Network” but had trouble generating interest in it. She took classes and attended ThrillerFest in New York City, a convention of top thriller writers, which so inspired her she urged Valerie to attend it with her the following year.

“She said, ‘I’m not a thriller writer,’” Lynne told Hearst Connecticut Media. “Little did she know she’d wind up as a thriller writer.”

It didn’t happen right away, though. The two penned a book of “women’s fiction” that failed to gain any traction. They hit their stride, and best-selling success, with “The Last Mrs. Parrish,” published in 2017. It gained notoriety as a Reese Witherspoon Hello Sunshine Book Club pick.

Then came “The Last Time I Saw You,” now being developed as a movie.

Lynne was always drawn to thrillers.

“I love Dean Koontz and Robin Cook. They pull you in and I find their work so transportive. There’s only so much you can do with other genres,” she said.

It turned out to be the perfect genre for the direction the sisters wanted to take.

“We both love exploring the psychology of people’s actions,” Lynne said. “For a long time I wanted to be a psychologist and criminal attorney. There’s always a new twist or new spin on a story. I find it very interesting.”

The Wife Stalker

“The Wife Stalker” is set in Westport, where Lynne lived for 10 years.

The story revolves around two women. Piper, a transplant from the West Coast, has a questionable past. “I’ve heard of Westport referred to as East Hollywood,” Lynne said. “I thought it was the perfect town to relocate from California. Having lived there it was much easier to write.”

The second character is Joanna, who is determined not to let Piper destroy her family. The book is written from both characters’ points of view, as each chapter alternates from one to the other.

“That’s something we have done in all our books,” she said. “It feels like for us, a better way to tell the story. So much is dependent on point of view. … You can tell the truth from one person’s point of view, but it may not be the real truth,” she said. By alternating characters, readers get more than one side of a story.

This approach works well because their books are character driven, more so than plot driven, Lynne said. Each character has a comprehensive backstory that includes their education, family, traumas and other experiences. Most of this never makes it into the book but it informs each character’s behavior.

None of the characters are based in large part on anyone they know.

“Life experience brings you a compilation of personalities to draw from,” Lynne said, adding with a laugh, “Since our books are about sociopaths, they are not people in our lives.”

Because their characters drive the story, “we don’t know exactly what’s going to happen,” she said. “We’re not outliners. We might have a certain path, but the characters definitely take on a life of their own. We always end up going back and rewriting the first chapter.”

Each of the sisters has strengths in writing certain areas. For Valerie it’s describing the setting, for Lynne it’s dialogue.

“We talk in the morning about who is going to write what,” Lynne explained. “If I want to go in a different direction, I have the freedom to do that. So far that has worked very well.”

The more they’ve worked together the more similar their writing styles have become. As they complete a section they read it to one another. They edit each other. By the time a book is published, each has reviewed every chapter, it’s gone through two or three revisions, and sometimes they can’t remember who wrote certain parts.

Because they are writing thrillers, there is considerable research they do either by reading or talking to experts such as FBI agents, police, psychologists, nurses and doctors. Lynne has even attended her town’s citizen’s police academy.

During the videoconference the sisters will be interviewed by author Wendy Walker. “There will be a Q&A and then we’ll open it up for questions,” Lynne said.

As for how she feels about these virtual events, she said, “I feel we’re reaching more people.” But being an extrovert, “I love being with people, talking with people. I would not want this to be the new normal.”

With that in mind, she invited readers to connect with them on livconstantine.com, Twitter and Facebook. “We love to hear from people,” she said.