Though guns aren't her literary weapon of choice, Oregon crime writer Chelsea Cain is a crack shot. "I prefer knives and razor blades," she says, and I might believe her if I hadn't just seen her add a third eye to the paper target from 20 feet away.

We're at a shooting range in Portland, trading off aiming a .22. Cain jokes we should have brought a poster of Gretchen Lowell, the serial killer in her series featuring Portland police detective Archie Sheridan (the fourth installment, The Night Season, is out from St. Martin's Minotaur) and his nemesis, Gretchen, who had kidnapped, tortured, and then released him all before the first book, Heartsick (2007). Thrown into the mix is newspaper reporter Susan Ward, the character Cain says she added because she can relate: "Like Susan, I've written those quirky newspaper features, have those weird clothes and drink a lot of red wine."

The cat-and-mouse game between cop and serial killer isn't new, but Cain's take on that normally antagonistic relationship is far from conventional. In fact, she describes the relationship between Archie and Gretchen as a "twisted love story." In Heartsick, Sweetheart (2008), and Evil at Heart (2009), Gretchen plays a large role as she taunts Archie from both inside and outside of prison, while in The Night Season her presence is mostly felt in Archie's mind. "I didn't want to have to do narrative acrobatics to work her in unnaturally," says Cain. "She escapes from prison! Again! She's caught! She escapes! I also wanted to evolve Archie and Susan's characters and relationship a bit." But Gretchen hasn't disappeared forever, Cain promises: "I love her too much."

With Gretchen on the sidelines, The Night Season should also entice new readers to the series who might otherwise be overwhelmed by the characters' complex backstories. "In some ways, it functions as a stand-alone," says Cain. "It works as a part of the series and as its own story, like an episode of Law & Order." The plot for this new book is based on a real-life event, the Vanport flood of 1948. "I'd lived in Portland on and off for a decade before I'd even heard of Vanport," says Cain. "It was this town of 20,000 people that washed away from north Portland. I'd taken my dogs to the dog park that is smack where Vanport used to be, but I had no idea that there had been a whole community that was leveled in a few hours." In The Night Season, Susan gets caught up in an article she's writing about Vanport after a skull is found at just such a dog park, while torrential rains threaten the city.

But water isn't the only unusual weapon in Cain's latest thriller. There's also the blue-ringed octopus, which Cain affectionately refers to as "my cephalopod." She explains: "The blue-ring octopus gets these fabulous neon blue rings all over its blobby little body when it's agitated. Beautiful, but deadly. Like the Pacific Northwest. Like Gretchen." In a Chelsea Cain book, death by octopus is tame in comparison to some of the havoc wrought by Gretchen, who carved a heart in Archie's chest and made him drink drain cleaner. Answering awkward questions about the violence in her books, particularly violence perpetrated by a woman and written about by a woman, Cain, 39, says the questions really baffle her. "I know that there's a cultural expectation that women be nurturing, delicate flowers. And I am. So delicate. But that doesn't mean I can't write a good, gory murder scene."

Indeed, The Night Season is decidedly less gory than its predecessors, as Cain admits. "But that's where the poisonous cephalopods and floodwaters come in: finding ways to generate thrills without all the disemboweled human tissue."

If Cain's books are a guide, the city of Portland is the perfect setting for a thriller. "Everything here is wet and rotting and covered with moss and mildew," Cain says. "And I say this as someone who loves Portland, loves rain, loves moss. I love the fact that we are surrounded by this spectacular natural beauty that routinely strikes us dead. Hikers walk off into the woods and are never seen again. And still we tug on our fleece and skip off into the wilderness, not a care in the world. And people think I'm the one who's mental."

Jordan Foster is a freelance writer in Portland, Ore.