Cassandra Clare first introduced the heroine of the Mortal Instruments series, Clary Fray, in City of Bones, where she falls in with the Shadowhunters of Manhattan and its Downworld (New York's "shadow self"). Now meet Tessa Gray, star of Clockwork Angel: Infernal Devices #1 (McElderry, $19.99, 9781416975861/1416975861, 496 pp., ages 12-up, August 31 laydown; also available on CD and for download from S&S Audio), which kicks off a companion series, set in London 130 years before Mortal Instruments. Tessa, an ordinary American girl, comes to London in search of her brother and is promptly kidnapped. "In this iteration, the Hell Fire Club inspired the Pandemonium Club," Clare explained. "They practice black magic and believe they can use Tessa for their nefarious purposes." Here the author talks about her fondness for cities and their shadow selves, trilogies and the parallels she has created between hers. 
Did you originally conceive of Mortal Instruments as a trilogy?
I did think of Mortal Instruments as a trilogy when I first constructed it because I was a huge fan of trilogies as a kid. There's a theme that runs through it that's [inspired by] Milton and The Divine Comedy. There are little epigraphs at the beginning of each section: the first is the hero's descent, the second is about hell and the underworld, and the third as an ascent out of the underworld. I think of it as Clary's heroic journey.
What drew you back to the series for City of Fallen Angels (to be released in April 2011)?
A graphic novel company asked if I could do a story set in the universe of Mortal Instruments, so I storyboarded out a concept for a new story that would take off from the end of City of Glass and focus slightly more on the character of Simon, Clary's best friend. The project fell through, so I went to Simon & Schuster and asked how they'd feel about me turning this into a novel. And they said, "But it's a trilogy!" And I said, "I think Scott Westerfeld has proven that a trilogy has four books."
Victorian-era London is quite a change from modern Manhattan.
I believe that all cities have a shadow self. [In Mortal Instruments,] I tried to use a lot of locations in Manhattan that were abandoned and no longer have a purpose. I lived in London for several years when I was growing up, and it's the city I know second-best to Manhattan. There are so many wonderful locations in London where there used to be something amazing in a spot that no longer exists, but some echo of it remains. That in particular interests me. There's a cemetery called the Cross Bones Graveyard across London Bridge where they buried prostitutes and single women in the 17th century, and it was razed in the early 1900s. Between two warehouses there's a chain-link fence with notes to the women who once were buried there. It says this was the resting place of the "unconsecrated dead."
How many books have you planned in the Infernal Devices series?
Three.
And will each book feature an Infernal Device, just as your Mortal Instruments each featured one of the three Mortal Instruments?
In this case, the Infernal Devices are the tools that the Pandemonium Club is working on that will destroy the Shadowhunters. There's a steampunk element to the novel because I love steampunk. I was trying to do a bit of paralleling, with the way Clary falls in with the Shadowhunters. Tessa's experience is different because she's a Downworlder. They sign the Accords so the Shadowhunters can live with Downworlders in an uneasy truce. In the Mortal Instruments series, the Accords were signed many years in the past. I wanted to set a book right after the Accords were signed, where the tensions are still really high between the Shadowhunters and Downworlders. Tessa showing up and being a Downworlder and yet being their only hope of defeating the Pandemonium Club creates a tension that wasn't there for Clary [in Mortal Instruments], because Clary was also a Shadowhunter.
How does your view of adolescence fit into the development of Tessa's gift to transform, and Clare's gift for the Sight?
One of the reasons we're often drawn to tell stories about adolescents who discover they're gifted in some special, often supernatural way, I think, is that they function well as allegory. It's the time in your life when you feel you don't belong and you're not like your parents, and you're not like anyone else, so who are you? And it's also the time when you discover that talent, that gift that makes you you.
And then for Clary and Jace there's the added layer of not knowing if you're related or not.
Yes, poor Clary and Jace. That was inspired by a story I read in a newspaper article. Two people were about to get married, and they had to get a blood test and discovered they were related and had been adopted out to two different families. I thought, this is a Greek tragedy dropped into modern times.
There's an interesting female-male trio dynamic in your books. Tessa Gray has male friends, Jem and Will; Clary has Simon and Jace.
I love a love triangle. With City of Bones, I didn't feel I'd done the classic love triangle. From the beginning Clary loves Jace, and Jace loves Clary. Clary never has feelings for Simon, so it's not the true love triangle in which love is equally balanced. With Will and Jem, Tessa's feelings are equally balanced. It's the love triangle that's calibrated carefully enough that you really don't know what's going to happen. Simon and Jace couldn't stand each other, but Will and Jem are best friends. For Tessa to come along and upset that delicate balance was also something I was interested in exploring.
Can you tell us anything else about the next books in the Infernal Devices trilogy?
When I decided to do City of Fallen Angels, I wanted to create stronger ties between Mortal Instruments and Infernal Devices, because I always enjoyed reading series that were related to each other. You can read the books in any order. Once you start reading City of Fallen Angels you'll begin to recognize the supernatural characters from Clockwork Angel. To me that kind of stuff is fun.
Be the first to read Clockwork Angel. Stop by the S&S booth (3940) at BEA on Thursday, May 27, at 9 a.m--only 300 ARCS will be available.