Christopher Farnsworth says it seemed like just another email from his agent.

But then Farnsworth, the author of thrillers such as “The President’s Vampire” and “Killfile,” opened it, and everything changed. That email was offering him the possibility of taking over the Jesse Stone series created by the late Robert B. Parker.

“It was nothing dramatic, not from the outside,” Farnsworth says by phone from his Los Angeles home. “But it was a big deal to me. My agent wrote me one day and said, ‘Hey, you’re a Robert Parker fan, right? They’re looking for a new guy for Jesse Stone — are you interested?’

“I immediately emailed her back and said, ‘Yes, absolutely. What do I have to do?’ You know, ‘Do you need an organ? Do you need blood, kidneys, what?’”

Parker is a legend in modern crime fiction. He wrote 40 thrillers about private detective Spenser over almost four decades, nine that featured police chief Jesse Stone, six with private investigator Sunny Randall, and three Westerns on the duo of Virgil Cole and Everett Hitch.

Since his death in 2010, all four series have continued with authors such as Ace Atkins, Mike Lupica, Reed Farrel Coleman and now Farnsworth breathing new life into the characters created by Parker.

For readers, it’s a way to keep connected to the stories they love. For writers, it’s a chance to step into the worlds dreamed up by Parker, an icon for many crime writers.

Even Parker knew the feeling: In 1989’s “Poodle Springs,” he channeled the persona of private eye Philip Marlowe for Raymond Chandler, who’d died 30 years earlier, taking the four chapters left by Chandler to complete the unfinished eighth Marlowe mystery.

Farnsworth’s agent went back to the Parker estate to say he was interested, but as someone who’d discovered Spenser as a teenager, he says he couldn’t — and didn’t — wait.

“I was so excited that I wrote the first chapter anyway,” he says. “I sent it to them, and apparently they liked it and thought it was good enough.”

“Robert B. Parker’s Buried Secrets” arrived in bookstores this month. Unlike Farnsworth’s earlier thrillers, which often incorporated elements of horror or the paranormal, “Buried Secrets” is a straightforward police procedural.

In it, Stone, the chief in the small, fictional Massachusetts town of Paradise, stumbles onto a dead man lying on a huge stash of cash inside his sofa, with boxes of files on murder victims stored in the clutter of his home.

As Stone and his officers investigate, an aging mob boss in Boston launches a handful of hit men to eliminate any evidence, and anyone who might discover the secrets the dead man kept.

In an interview edited for length and clarity, Farnsworth talked about what it was like to step into Parker’s shoes, his inspiration for the first chapter of the book, why it was fun to write a book that didn’t involve vampires and other secret abilities, and more.

Q So I’d guess you’ve been reading Parker books for a long time.

A I’ve been a fan since I was reading “Spenser” in high school. I won’t say I’m as rabid as some of the fans out there, but I was always impressed with his ability to not only create a compelling story and compelling characters but to do the P.I. novel in a way that was different. And with Jesse, to do the cop novel in a way that was different. Also, he was funny.

He was like a gateway drug into all these other really incredible writers that I didn’t know about at the time, like Gregory McDonald and the Fletch novels. The Lew Archer novels by Ross Macdonald, and Marlowe and just the classics.

Q I liked the “Spenser: For Hire” TV series in the ’80s — did you watch it?

A I didn’t watch it a lot, but I think that’s how I knew what Spenser was. I’ve written about this before, but my library was the spinner rack in the grocery store, the drugstore. So I read a lot of pulp fiction. Somebody, my mom or my dad, left a copy of “Spenser” lying around and I picked that up.

Q All of your books before this are originals. What did it take to shift from your own creations into the universe of Jesse Stone?

A I think the first most important thing is to do the homework. To read everything you haven’t read before. I’d read a lot of Parker, I’d read a lot of Spenser, but I had not read everything of Jesse Stone, so I wanted to make sure I had the continuity down.

You know I’m a comic book geek, and that’s an important thing, even outside the world of comics. When you’re working in a shared universe it’s important to get the details right, because it means a lot to a lot of fans out there. They’ve invested their time and attention to this character, and they’re going to know if you got it wrong. So I read or reread the entire series, including the series from other authors, to get more of an idea how Jesse has evolved.

Q What did you find?

A I think Jesse is different than Spenser in really one important way. I’ve said this before, but Spenser is Parker’s perfect knight. He’s Galahad. Despite being a flawed man in a flawed world, he can bear the weight of the moral code that Parker weaves through all of his books. Of doing the right thing, of always being honest, of saying what you mean and keeping your word no matter what.

What I realized is that is an incredible burden to have to carry. How many times do you tell little white lies? Do little things to be polite? Grease the wheels to make getting through life easier? And Spenser doesn’t do that. He doesn’t take the easy way out.

The thing is, neither does Jesse Stone, but Jesse feels the weight of it much more. He’s not a perfect knight. He’s a flawed man trying to be a good man, but the pain of it has hurt and crippled him at times, which is why he spent so many years as a drunk. I think what’s really interesting about how Parker created Jesse Stone is it seems like he created him to be a person who could grow and learn.

Q When you take a project like this, does the estate have guidelines about what you can do? I don’t think they’d have to tell you, “Please don’t kill off Jesse Stone —”

A God, hopefully not! (Laugh.) “Oh yeah, I kill him. Page 15, it’s over. Real shocker.” No, actually the estate, and the agent of the estate, Esther Newberg, were completely hands-off. They trust people. It was really a great compliment, and a little daunting at the same time, because you’re not given any rails or guidelines to keep you in line.

You have to know how far to take it, and you also have to respect what came before you, knowing that it’s not your thing. Like, my books, I kill people all the time. Just bodies are dropping, it’s a massacre and it doesn’t matter. I’ve had people tell me, “I really like that character; I wish they were still around.” I’m like, “Yeah, that’s too bad. They had to go.” Obviously, you can’t do that in Jesse Stone, but I was impressed and flattered that they give you the freedom to set your own course.

Q When you read all the Stone books, could you see differences in the writing as they shifted from Parker to Michael Brandman to Reed Farrel Coleman to Mike Lupica? I’m curious how you handled that.

A I think you have to find a careful balance. No writer is capable of writing as anything but themselves, really. You are always going to default to your own quirks and style in some areas, and I think I’ve done that in this book. There is some stuff that’s definitely me.

I tried to be — one of Parker’s great gifts is that he’s funny. And he’s got a great sense of timing. I was talking about this with another writer friend of mine, Ben Winters, who is also a Parker fan, and he was saying it’s just amazing the way the chapters have their own rhythm, and they always end on such a great punch.

Like, it takes your breath. It hits you in the gut and then it launches you into the next chapter. So I really tried to do that. Whether I succeeded or not, that’s up to the fans.

Q I know you’ve written screenplays as well as novels, and it occurred to me that might be useful in taking on an existing series, which seems like it might be similar to adapting a book for a screenplay.

A I think that’s a good way of putting it. This is the adaptation of a movie that doesn’t exist yet, or a book that hadn’t been written. I hadn’t really thought about it but I do think that was a skill that was helpful. Because in screenwriting, you’re an employee and you’re doing work for somebody else always. So you learn to be less, I don’t know, precious or controlling about it. You learn to let go of some stuff.

When I first started screenwriting, I was handed a lot of books and told, “Hey, see if you can turn this into a script.” You have to learn what to hang on to and what to let go of. But it’s somebody else’s work.

Q I want to go back to that first chapter you wrote and sent in. Was that scene with Jesse going into the house and finding the dead man something you’d been thinking about already?

A Well, about 10 years ago, we had a knock on the door, and it was a friend of a next-door neighbor saying, “Have you guys seen him recently? Because I haven’t seen him for a few weeks.” I had to hop the fence and went over, and the back sliding door was open. I went in — and you’re a reporter, I’m a reporter — we have both seen dead bodies, unfortunately. So I knew the smell in the house, which was packed to the rafters with junk, stacks of phone books, cases of motor oil, newspapers and flyers for decades.

I came back out and told his friend, let’s just sit here and I’ll wait with you for the police. And because writers are terrible, terrible people, I always knew I was going to use that in a book.

Q I think this is your most straight-ahead crime thriller — no vampires or special gifts. What was it like to leave those things aside for this one?

A It was, honestly, a relief. (Laughs.) With my other stuff, you have to come up with all these rules. They have to be consistent and you have to create a whole universe. You also have to make your protagonist strong enough to be special but not so strong that nothing can stop them, otherwise it’s not challenging.

And what I discovered was just cops and robbers and hit men is actually a lot. The rules are established and it’s much easier. It’s actually a lot of fun to play within those ropes like it’s a boxing ring or a wrestling ring. You can bounce off them. You can do all kinds of cool stuff inside the ring, but you stay inside the ring.