Have you ever seen a pregnant woman, perhaps with her arms weighed down by shopping bags, digging through her purse in front of a heavy door—and rushed forward to let her in using your own keycard? Or perhaps found a stray USB drive on the floor in your office building—and plugged it into your computer to see if you could figure out who to return it to?

If the answer to either or both questions is yes, you might have done someone a big favor . . . or you might have fallen prey to a penetration tester. Pen testers, as they’re often called, are daring and creative sorts hired by companies to identify security vulnerabilities, help repair weaknesses in their systems and recommend practices for avoiding issues in the future. That might involve attempting to access a vitally important database or evading security guards after sneaking into a presumably well-secured building.

A husband-and-wife pen tester team is at the center of Ruth Ware’s propulsive and emotionally complex new thriller, Zero Days. Gabe and Jack (short for Jacintha) revel in the complicated challenges and thrills that come with performing legally sanctioned digital and physical break-ins for their clients. 

Ware revels in it, too; the internationally bestselling author’s deep fascination with the subject is evident in the wealth of intriguing details and scenarios that make Zero Days, her eighth novel, a supremely suspenseful reading experience. In a call with BookPage from her home on the south coast of England, where she lives with her husband and two children, the author says that she got hooked on the idea of writing about pen testers while performing in-depth research for two of her previous books. 

“I had been researching apps and startups and tech companies for The Turn of the Key and One by One,” she explains. “I started listening to a lot of tech startup podcasts, and then from there I just gravitated toward the crime-y stabby edge. . . . I ended up on the darknet end of the internet, and that was where I first found out about pen testers and the extent of what they do.” 

She also listened to “hundreds of hours of podcasts, read blogs, memoirs, online articles and interviews and so on,” she says. “Usually my process of research is to dredge as widely as I can and absorb as much as I can, and then at the end maybe 5% of that makes it into the book.” This immersive process helps her “paint the picture of the person who would do this job, what’s their day-to-day life like, what are all the interesting little nuggets of weirdness that are going to make it into the book.”

Jack’s keen ability to strategize and adapt under pressure is essential to her role—and, tragically, becomes necessary for her very survival. One night, while Jack is completing an assignment, Gabe is brutally murdered in their home. Not only does Jack lose her beloved life partner but the police consider her the prime suspect. Knowing that as long as they’re focusing on her they won’t search for the real killer, Jack decides to run for it: She’ll do her utmost to evade capture while figuring out who the real murderer is, and hopefully exact some vengeance along the way.

It’s a decision that makes complete sense for the character, of course, but what about the woman who created her? Ware insists with a laugh that “I wouldn’t make that decision in a million years. I would hunker down and hope to god that everything was sorted out. I wouldn’t trust myself to think, well, I can investigate this better than the police, whereas I think Jack genuinely does think that. And to an extent, she’s going to be right because of her unique skill set.”

The author also notes that Jack’s preternatural confidence in all manner of sticky situations is not something she possesses. “I am superaware of my own limitations,” she says. “I am an incredibly bad liar, which is a strange thing for a writer to say. . . . I’m very law-abiding. If I have the least consciousness of guilt, I go scarlet. That’s how I know I could never do that job. I could never walk into somewhere where I didn’t belong and act like I did.”

Jack, on the other hand, can and does, and when she takes to the streets of London—home to one of the most extensive CCTV surveillance systems in the world—that capability is crucial. But while she does fall on the more-prepared side of things, even in particularly dicey circumstances, she is also fallible, subject to misguided impulses, nagging injuries and uncertainty about what to do next.

“The temptation when you’re writing is always to go a little bit more Mission: Impossible, a little bit more Ethan Hunt, sliding down lift shafts and such, and the dramatic part of me would have loved to write some of those things,” Ware says. “But it was also really important to me to root it in the reality of what these jobs are, which is that, yes, it does take a certain type of personality, but actually you don’t have to be at the pinnacle of fitness or have a genius IQ. . . . You need to be very confident and very charming and able to push the envelope a little bit more than someone else might.”

Jack also struggles under the weight of immense shock and grief. Her deep sadness over the incomprehensible loss of Gabe comes in waves throughout Zero Days. It’s something she isn’t able to fully process, what with the police, and possibly the people who killed Gabe, close on her tail. 

That sorrowful refrain was crucial, Ware says, when it came to imbuing her time-is-running-out tale with a mournful yet determined heart. “Probably the biggest critique I have of Golden Age crime [fiction], and modern crime as well, is that sometimes the death of the person whose murder forms the mystery at the heart of the book can be treated like it’s just there to provide the puzzle or the impetus for the main character,” she says. 

“Thank god I’ve never really lost anyone in my life in the way that Jack loses Gabe, but I have been bereaved,” Ware adds, “and it is a seismic life event that you do not get over quickly; you’re not out there merrily detecting two weeks later. I wanted to be really careful to show the effects that grief has on a life and the ripples of consequence. . . . That’s true to how I think we are as people, we carry on putting one foot in front of the other because we have to and the world does go on . . . but every now and again you get hit by the reality of what happened.”

In terms of achieving practical verisimilitude in her story, Ware turned to a British reality TV show. “When I was researching, I spoke to a number of police officers,” she says, “and they all said the same thing: You should watch ‘Hunted.’” The action-packed goings-on in the show, which follows 14 people as they try to remain hidden for 28 days while a team of experts attempts to track them down, vividly illustrate the speed at which paranoia can build and how easily one can be found via elements of modern life such as online banking. 

Another aspect of the show resonated with Ware on a deeper level. “The ones who win are usually successful because they’re likable people and they persuade people to do nice things for them,” she says. “And it just constantly amazes me how willing people are to go the extra mile for total strangers.” 

That revelation was, happily, in keeping with her own convictions. “I wanted to show both sides of that in the book. Jack’s a suspicious person; she has to be because of her job, and being on the run is only exacerbating that, “ Ware says. “But at the same time, I think human beings are much lovelier and kinder than we give them credit for.”

Even as we celebrate the good in humanity, though, Ware warns that we should not be cavalier about protecting ourselves online. After all, as Jack muses in Zero Days, there are most definitely bad actors lurking around the internet: “slippery, shadowy, forcing their way through the cracks in our online security and the doors we left open for them in our digital lives.” 

When I tell Ware that this poetically stated line is quite the chilling sentiment, she replies with a cheery “Thank you!” and adds, “I think once it comes out, if anyone takes any moral or lesson from this book, it should be to use a password manager.” That’s because, she explains, “reusing passwords is the equivalent of chaining all your door keys and car keys in the same bunch and then putting your address on it,” while a password manager generates and stores unique passwords for the myriad accounts we all juggle every day. “Literally every single person I interviewed said this,” the author says. And by the way, she laughs, “I was already using a password manager, so I felt very smug.”

While she’s justifiably pleased with herself when it comes to online savvy, Ware is far from smug about her career thus far. Since her first book, In a Dark, Dark Wood, was published in 2015, her books (more than 6 million in print, and counting) have been published in more than 40 languages worldwide. “I never expected to have this level of success. . . . There are moments when it’s brought home to me very forcibly; when I walk into a place full of readers who are there for me, it’s wonderful and terrifying.” But, she says, “when I’m actually at my desk writing, it’s something I try not to think about too much. . . . For me, every book is really a process of tricking myself into believing that nobody apart from me is going to read it.” 

Of course, that’s extremely unlikely to happen with Zero Days, which Ware says is a bit of a departure from her typical fare. “I don’t want to sit down and think, what would be the next Agatha Christie-ish Ruth Ware book that I could write?” she says. “It’s much more about finding something I want to say, and then hopefully at the end of that people will like it and my publishers will be able to market it. Which is exactly how this book came about, with me becoming mildly obsessed with the subject and my imagination running away with me, and then at the end of it thinking, oh gosh, I think I’ve written a thriller!” 

Indeed she has, one that will have readers rooting for Jack as they strategize survival and try to ferret out the truth right along with her. Presumably, they’ll also gather up tips that will come in handy should they one day become embroiled in a similar pickle—or even be inspired to become pen testers themselves. And all the while, Ware hopes, “I would like us to be a little bit less suspicious of each other as individuals, because I think the world has mostly good people, but a little bit more careful with our online security overall.” In other words: Get thee a password manager!

Photo of Ruth Ware by Gemma Day Photography.