Thirteen years ago, Cassandra Clare launched her bestselling Mortal Instruments trilogy with City of Bones, a YA urban fantasy novel about demon-slaying Nephilim known as Shadowhunters. This March, Clare kicks off her fifth Shadowhunters series, The Last Hours trilogy, with Chain of Gold. PW spoke with Clare regarding her ever-expanding fictional universe, character diversity, time management, and her first foray into adult fantasy.

With the publication of Chain of Gold, which launches the Last Hours trilogy, you’ve now got five different series set in the Shadowhunters universe, spanning almost 150 years. How do you keep track of all the intersecting plot lines, timelines, and family trees?

The process of keeping track of everything has definitely changed along the way. With the first books, the universe wasn’t as expansive as it is now; I kept notes in a notebook, but I wasn’t incredibly methodical. Then, at some point, I decided that I wanted to put together a Shadowhunters Codex. Within the world of the books, when a Shadowhunter becomes old enough to go out and hunt demons and whatnot, they’re given a Shadowhunters Codex, which is a list of rules and regulations that the Shadowhunter world has, and has some of the Shadowhunter history in it. I thought it would be a fun project to put together one of those so that readers could, if they wanted to, have their own Codex.

As I did that, I realized how scattered my notes were. I was working on it with my husband, Josh, and he’d be like, “Okay, where’s the stuff about this?” And I’d be like, “Umm, it’s on my computer, in a file called ‘miscellaneous....’ ” I needed to get more organized, so I went through all the books. I tabbed them with different colors, which corresponded to things like history, weapons, characters, lineage, magic, things like that, and then from that, I sort of built out the Shadowhunters Codex. I also created for myself a thing that my assistant and I now call the bible, which is sort of a giant virtual notebook that has all of that information in it.

You seem to publish at least two books a year, which means you must constantly find yourself plotting one book while editing another. How do you manage to compartmentalize, and to hit your deadlines?

For me, it requires a lot of discipline to work quickly. What I’ve learned over the years is to outline carefully before I write, and work out the kinks in the story before I get to the process of writing it. I’m not working out every scene or emotional beat, but I’m kind of saying, “This is what happens, this is what happens….” B follows on A, and C follows on B. I’m working out the A, B, C, D part of it, so when I sit down to write, hopefully I don’t suddenly get caught short by information I don’t have or a problem in the story.

And in terms of keeping the books and the worlds separate, I never work on more than one book at the same time. I find it difficult to switch back and forth between them. I know some people can [work on two books] on the same day, but I can’t, and when I figured that out, I was like, “Okay, so what I’m going to need to do is cut it into dedicated chunks of time that are at least three or four weeks long.” So I work on book A, then switch over to working on book B, and I don’t edit one book while writing another.

The cast of Chain of Gold—and the Shadowhunters organization, in general—comprises characters of sundry species, ethnicities, abilities, and sexual orientations. Why is character diversity so important to you, and how do you avoid stereotype when writing them?

For me, character diversity is important because my readership is very diverse, and I tend to be pretty close with them, and often answer questions and talk to them at signings and on social media. One of the things that was important to me was for people to feel that—regardless of gender, sexual orientation, ethnicity, religion, ability—everyone is able to be a Shadowhunter if they want to. I recall when I was a kid reading the Narnia books and having the realization that, as a Jewish kid, I was not welcome in Narnia. That was a really terrible feeling, and I didn’t want to give that feeling to anybody else. That was more significant than my own worry about writing outside what I know.

So what I do is I contact members of the marginalized community that I am writing about, and run what I’m writing by them. It’s obviously not the burden of your sensitivity reader to fix your book, but I think that we all can fall into unconscious stereotyping even when we’re trying really hard not to. And also, we can fall into things that we didn’t know were stereotypes. When I wrote a transgender character in The Dark Artifices, before I ever started the book, I reached out to the transgender community in my area. I met with many trans women and talked with them before I even started writing, so that I could more carefully and sensitively build that character. Of course, any mistakes are mine, but I feel that while research in journals, in books, and online is certainly valuable, it is important to reach out to members of the community that you’re trying to represent.

The Shadowhunter books are YA fantasy, and you collaborated with Holly Black on the Magisterium Series, which is middle-grade fantasy. Do you have any plans to write adult fantasy one day?

I do! I have two books coming out with Random House. The first one comes out next year, and it’s called Sword Catcher. It’s an adult high fantasy novel, and it’s been a really different experience working on it. Shadowhunters books are set in various cities all over the world, so [in order to write them,] I’ll have to do research on Paris in 1903 and London in 1878. With high fantasy, I have to make up everything, down to the street signs. So, I have had that experience of writing high fantasy for the first time, and also the experience of writing adult characters who have different concerns, and think about things differently. In these books, I have to plunge into the immediacy of what it feels like to be a character who is an adult and has very different concerns than they would have if they were a teenager. With both middle grade and YA, there is a lot of concentration on family and parents because those are your primary relationships; our parents, our parents’ opinions of us, and our relationships with them shape big parts of our lives when we’re young adults. I had to move into a phase where people’s primary relationships are going to be with colleagues, and with husbands and wives, and even with their own children, so that was definitely an adjustment. It’s been fascinating, and really fun to stretch myself as a writer in that way.

Chain of Gold (The Last Hours #1) by Cassandra Clare. McElderry, $24.99 Mar. 3 ISBN 978-1-4814-3187-3